Run these commands on each switch to change the hostname and bring up the interfaces. Exit the switch, then log back in to see the new hostname at the prompt.
cumulus@cumulus:mgmt:~$ net add hostname leaf01 cumulus@cumulus:mgmt:~$ net add interface swp1,swp2,swp3 cumulus@cumulus:mgmt:~$ net commit cumulus@cumulus:mgmt:~$ exit
cumulus@cumulus:mgmt:~$ net add hostname leaf02 cumulus@cumulus:mgmt:~$ net add interface swp1,swp2,swp3 cumulus@cumulus:mgmt:~$ net commit cumulus@cumulus:mgmt:~$ exit
cumulus@cumulus:mgmt:~$ net add hostname spine01 cumulus@cumulus:mgmt:~$ net add interface swp1,swp2 cumulus@cumulus:mgmt:~$ net commit cumulus@cumulus:mgmt:~$ exit