diff --git a/features/cart/shopping_cart/changing_quantity_of_product_in_cart.feature b/features/cart/shopping_cart/changing_quantity_of_product_in_cart.feature
index fe83b0f6dff..64f739c748b 100644
--- a/features/cart/shopping_cart/changing_quantity_of_product_in_cart.feature
+++ b/features/cart/shopping_cart/changing_quantity_of_product_in_cart.feature
@@ -9,14 +9,14 @@ Feature: Changing quantity of a product in cart
         And the store has a product "T-shirt banana" priced at "$12.54"
         And I add this product to the cart
 
-    @ui
+    @ui @api
     Scenario: Increasing quantity of an item in cart
         Given I see the summary of my cart
-        When I change "T-shirt banana" quantity to 2
+        When I change product "T-shirt banana" quantity to 2 in my cart
         Then I should see "T-shirt banana" with quantity 2 in my cart
 
-    @ui
+    @ui @api
     Scenario: Increasing quantity of an item in cart beyond the threshold
         Given I see the summary of my cart
-        When I change "T-shirt banana" quantity to 20000
+        When I change product "T-shirt banana" quantity to 20000 in my cart
         Then I should see "T-shirt banana" with quantity 9999 in my cart
diff --git a/src/Sylius/Behat/Context/Api/Shop/CartContext.php b/src/Sylius/Behat/Context/Api/Shop/CartContext.php
index b400bd82702..773c45ea4fb 100644
--- a/src/Sylius/Behat/Context/Api/Shop/CartContext.php
+++ b/src/Sylius/Behat/Context/Api/Shop/CartContext.php
@@ -83,22 +83,22 @@ public function iAddOfThemToMyCart(int $quantity, ProductInterface $product, str
         $this->putProductToCart($product, $tokenValue, $quantity);
     }
 
+    /**
+     * @When /^I change (product "[^"]+") quantity to (\d+) in my (cart)$/
+     */
+    public function iChangeQuantityToInMyCart(ProductInterface $product, int $quantity, string $tokenValue): void
+    {
+        $itemId = $this->geOrderItemIdForProductInCart($product, $tokenValue);
+        $this->changeQuantityOfOrderItem($itemId, $quantity, $tokenValue);
+    }
+
     /**
      * @When /^I remove (product "[^"]+") from the (cart)$/
      */
     public function iRemoveProductFromTheCart(ProductInterface $product, string $tokenValue): void
     {
-        $items = $this->responseChecker->getValue($this->cartsClient->show($tokenValue), 'items');
-
-        foreach ($items as $item) {
-            $pathElements = explode('/', $item['variant']['product']);
-
-            $productCode = $pathElements[array_key_last($pathElements)];
-
-            if ($product->getCode() === $productCode) {
-                $this->removeOrderItemFromCart((string) $item['id'], $tokenValue);
-            }
-        }
+        $itemId = $this->geOrderItemIdForProductInCart($product, $tokenValue);
+        $this->removeOrderItemFromCart($itemId, $tokenValue);
     }
 
     /**
@@ -244,4 +244,33 @@ private function getProductForItem(array $item): Response
 
         return $this->productsClient->show(StringInflector::nameToSlug($productCode));
     }
+
+    private function getOrderItemProductCode(array $item): string
+    {
+        $pathElements = explode('/', $item['variant']['product']);
+
+        return $pathElements[array_key_last($pathElements)];
+    }
+
+    private function geOrderItemIdForProductInCart(ProductInterface $product, string $tokenValue): ?string
+    {
+        $items = $this->responseChecker->getValue($this->cartsClient->show($tokenValue), 'items');
+
+        foreach ($items as $item) {
+            if ($product->getCode() === $this->getOrderItemProductCode($item)) {
+                return  (string) $item['id'];
+            }
+        }
+
+        return null;
+    }
+
+    private function changeQuantityOfOrderItem(string $orderItemId, int $quantity, string $tokenValue): void
+    {
+        $request = Request::customItemAction('orders', $tokenValue, HttpRequest::METHOD_PATCH, 'change-quantity');
+
+        $request->updateContent(['orderItemId' => $orderItemId, 'newQuantity' => $quantity]);
+
+        $this->cartsClient->executeCustomRequest($request);
+    }
 }
diff --git a/src/Sylius/Behat/Context/Ui/Shop/CartContext.php b/src/Sylius/Behat/Context/Ui/Shop/CartContext.php
index 49911c175a5..633c9424ef1 100644
--- a/src/Sylius/Behat/Context/Ui/Shop/CartContext.php
+++ b/src/Sylius/Behat/Context/Ui/Shop/CartContext.php
@@ -90,6 +90,7 @@ public function iRemoveProductFromTheCart(string $productName): void
 
     /**
      * @Given I change :productName quantity to :quantity
+     * @Given I change product :productName quantity to :quantity in my cart
      */
     public function iChangeQuantityTo($productName, $quantity)
     {
diff --git a/src/Sylius/Bundle/ApiBundle/Command/Cart/ChangeItemQuantityInCart.php b/src/Sylius/Bundle/ApiBundle/Command/Cart/ChangeItemQuantityInCart.php
new file mode 100644
index 00000000000..0adecc1bda8
--- /dev/null
+++ b/src/Sylius/Bundle/ApiBundle/Command/Cart/ChangeItemQuantityInCart.php
@@ -0,0 +1,59 @@
+<?php
+
+/*
+ * This file is part of the Sylius package.
+ *
+ * (c) Paweł Jędrzejewski
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Sylius\Bundle\ApiBundle\Command\Cart;
+
+use Sylius\Bundle\ApiBundle\Command\OrderTokenValueAwareInterface;
+
+final class ChangeItemQuantityInCart implements OrderTokenValueAwareInterface
+{
+    /** @var string|null */
+    public $orderTokenValue;
+
+    /**
+     * @var string
+     * @psalm-immutable
+     */
+    public $orderItemId;
+
+    /**
+     * @var int
+     * @psalm-immutable
+     */
+    public $newQuantity;
+
+    public function __construct(string $orderItemId, int $newQuantity)
+    {
+        $this->orderItemId = $orderItemId;
+        $this->newQuantity = $newQuantity;
+    }
+
+    public static function createFromData(string $tokenValue, string $orderItemId, int $newQuantity): self
+    {
+        $command = new self($orderItemId, $newQuantity);
+
+        $command->orderTokenValue = $tokenValue;
+
+        return $command;
+    }
+
+    public function getOrderTokenValue(): ?string
+    {
+        return $this->orderTokenValue;
+    }
+
+    public function setOrderTokenValue(?string $orderTokenValue): void
+    {
+        $this->orderTokenValue = $orderTokenValue;
+    }
+}
diff --git a/src/Sylius/Bundle/ApiBundle/CommandHandler/Cart/ChangeItemQuantityInCartHandler.php b/src/Sylius/Bundle/ApiBundle/CommandHandler/Cart/ChangeItemQuantityInCartHandler.php
new file mode 100644
index 00000000000..07120781910
--- /dev/null
+++ b/src/Sylius/Bundle/ApiBundle/CommandHandler/Cart/ChangeItemQuantityInCartHandler.php
@@ -0,0 +1,66 @@
+<?php
+
+/*
+ * This file is part of the Sylius package.
+ *
+ * (c) Paweł Jędrzejewski
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Sylius\Bundle\ApiBundle\CommandHandler\Cart;
+
+use Sylius\Bundle\ApiBundle\Command\Cart\ChangeItemQuantityInCart;
+use Sylius\Component\Core\Model\OrderInterface;
+use Sylius\Component\Core\Model\OrderItemInterface;
+use Sylius\Component\Order\Modifier\OrderItemQuantityModifierInterface;
+use Sylius\Component\Order\Processor\OrderProcessorInterface;
+use Sylius\Component\Order\Repository\OrderItemRepositoryInterface;
+use Symfony\Component\Messenger\Handler\MessageHandlerInterface;
+use Webmozart\Assert\Assert;
+
+final class ChangeItemQuantityInCartHandler implements MessageHandlerInterface
+{
+    /** @var OrderItemRepositoryInterface */
+    private $orderItemRepository;
+
+    /** @var OrderItemQuantityModifierInterface */
+    private $orderItemQuantityModifier;
+
+    /** @var OrderProcessorInterface */
+    private $orderProcessor;
+
+    public function __construct(
+        OrderItemRepositoryInterface $orderItemRepository,
+        OrderItemQuantityModifierInterface $orderItemQuantityModifier,
+        OrderProcessorInterface $orderProcessor
+    ) {
+        $this->orderItemRepository = $orderItemRepository;
+        $this->orderItemQuantityModifier = $orderItemQuantityModifier;
+        $this->orderProcessor = $orderProcessor;
+    }
+
+    public function __invoke(ChangeItemQuantityInCart $command): OrderInterface
+    {
+        /** @var OrderItemInterface|null $orderItem */
+        $orderItem = $this->orderItemRepository->findOneByIdAndCartTokenValue(
+            $command->orderItemId,
+            $command->orderTokenValue
+        );
+
+        Assert::notNull($orderItem);
+
+        /** @var OrderInterface $cart */
+        $cart = $orderItem->getOrder();
+
+        Assert::same($cart->getTokenValue(), $command->orderTokenValue);
+
+        $this->orderItemQuantityModifier->modify($orderItem, $command->newQuantity);
+        $this->orderProcessor->process($cart);
+
+        return $cart;
+    }
+}
diff --git a/src/Sylius/Bundle/ApiBundle/Resources/config/api_resources/Order.xml b/src/Sylius/Bundle/ApiBundle/Resources/config/api_resources/Order.xml
index 06850db2854..ca92d0393f0 100644
--- a/src/Sylius/Bundle/ApiBundle/Resources/config/api_resources/Order.xml
+++ b/src/Sylius/Bundle/ApiBundle/Resources/config/api_resources/Order.xml
@@ -143,6 +143,20 @@
                     <attribute name="groups">cart:remove_item</attribute>
                 </attribute>
             </itemOperation>
+
+            <itemOperation name="change_quantity">
+                <attribute name="security">is_granted('IS_AUTHENTICATED_ANONYMOUSLY')</attribute>
+                <attribute name="openapi_context">
+                    <attribute name="summary">Change quantity of order item</attribute>
+                </attribute>
+                <attribute name="method">PATCH</attribute>
+                <attribute name="path">/orders/{id}/change-quantity</attribute>
+                <attribute name="messenger">input</attribute>
+                <attribute name="input">Sylius\Bundle\ApiBundle\Command\Cart\ChangeItemQuantityInCart</attribute>
+                <attribute name="denormalization_context">
+                    <attribute name="groups">cart:change_quantity</attribute>
+                </attribute>
+            </itemOperation>
         </itemOperations>
 
         <property name="id" identifier="false" writable="false" />
diff --git a/src/Sylius/Bundle/ApiBundle/Resources/config/serialization/Commands/Cart/ChangeItemQuantityInCart.xml b/src/Sylius/Bundle/ApiBundle/Resources/config/serialization/Commands/Cart/ChangeItemQuantityInCart.xml
new file mode 100644
index 00000000000..30394dfd163
--- /dev/null
+++ b/src/Sylius/Bundle/ApiBundle/Resources/config/serialization/Commands/Cart/ChangeItemQuantityInCart.xml
@@ -0,0 +1,27 @@
+<?xml version="1.0" ?>
+
+<!--
+
+ This file is part of the Sylius package.
+
+ (c) Paweł Jędrzejewski
+
+ For the full copyright and license information, please view the LICENSE
+ file that was distributed with this source code.
+
+-->
+
+<serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
+>
+    <class name="Sylius\Bundle\ApiBundle\Command\Cart\ChangeItemQuantityInCart">
+        <attribute name="orderItemId">
+            <group>cart:change_quantity</group>
+        </attribute>
+
+        <attribute name="newQuantity">
+            <group>cart:change_quantity</group>
+        </attribute>
+    </class>
+</serializer>
diff --git a/src/Sylius/Bundle/ApiBundle/Resources/config/services/command_handlers.xml b/src/Sylius/Bundle/ApiBundle/Resources/config/services/command_handlers.xml
index 1995f8f1c1c..be48bcc0d4c 100644
--- a/src/Sylius/Bundle/ApiBundle/Resources/config/services/command_handlers.xml
+++ b/src/Sylius/Bundle/ApiBundle/Resources/config/services/command_handlers.xml
@@ -77,5 +77,12 @@
             <argument type="service" id="sm.factory" />
             <tag name="messenger.message_handler" />
         </service>
+
+        <service id="Sylius\Bundle\ApiBundle\CommandHandler\Cart\ChangeItemQuantityInCartHandler">
+            <argument type="service" id="sylius.repository.order_item" />
+            <argument type="service" id="sylius.order_item_quantity_modifier" />
+            <argument type="service" id="sylius.order_processing.order_processor" />
+            <tag name="messenger.message_handler" />
+        </service>
     </services>
 </container>
diff --git a/src/Sylius/Bundle/ApiBundle/spec/CommandHandler/Cart/ChangeItemQuantityInCartHandlerSpec.php b/src/Sylius/Bundle/ApiBundle/spec/CommandHandler/Cart/ChangeItemQuantityInCartHandlerSpec.php
new file mode 100644
index 00000000000..69047747c4d
--- /dev/null
+++ b/src/Sylius/Bundle/ApiBundle/spec/CommandHandler/Cart/ChangeItemQuantityInCartHandlerSpec.php
@@ -0,0 +1,62 @@
+<?php
+
+/*
+ * This file is part of the Sylius package.
+ *
+ * (c) Paweł Jędrzejewski
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace spec\Sylius\Bundle\ApiBundle\CommandHandler\Cart;
+
+use PhpSpec\ObjectBehavior;
+use Sylius\Bundle\ApiBundle\Command\Cart\ChangeItemQuantityInCart;
+use Sylius\Bundle\OrderBundle\Doctrine\ORM\OrderItemRepository;
+use Sylius\Component\Core\Model\OrderInterface;
+use Sylius\Component\Core\Model\OrderItemInterface;
+use Sylius\Component\Order\Modifier\OrderItemQuantityModifierInterface;
+use Sylius\Component\Order\Processor\OrderProcessorInterface;
+use Sylius\Component\Order\Repository\OrderItemRepositoryInterface;
+use Symfony\Component\Messenger\Handler\MessageHandlerInterface;
+
+final class ChangeItemQuantityInCartHandlerSpec extends ObjectBehavior
+{
+    function let(
+        OrderItemRepositoryInterface $orderItemRepository,
+        OrderItemQuantityModifierInterface $orderItemQuantityModifier,
+        OrderProcessorInterface $orderProcessor
+    ) {
+        $this->beConstructedWith($orderItemRepository, $orderItemQuantityModifier, $orderProcessor);
+    }
+
+    function it_is_a_message_handler(): void
+    {
+        $this->shouldImplement(MessageHandlerInterface::class);
+    }
+
+    function it_changes_order_item_quantity(
+        OrderItemRepositoryInterface $orderItemRepository,
+        OrderItemQuantityModifierInterface $orderItemQuantityModifier,
+        OrderProcessorInterface $orderProcessor,
+        OrderInterface $cart,
+        OrderItemInterface $cartItem
+    ): void {
+        $orderItemRepository->findOneByIdAndCartTokenValue(
+            'ORDER_ITEM_ID',
+            'TOKEN_VALUE'
+        )->willReturn($cartItem);
+
+        $cartItem->getOrder()->willReturn($cart);
+
+        $cart->getTokenValue()->willReturn('TOKEN_VALUE');
+
+        $orderItemQuantityModifier->modify($cartItem, 5)->shouldBeCalled();
+        $orderProcessor->process($cart)->shouldBeCalled();
+
+        $this(ChangeItemQuantityInCart::createFromData( 'TOKEN_VALUE', 'ORDER_ITEM_ID', 5));
+    }
+}