1) Change the IP address of a VLAN interface
(Aruba620) (config) #interface vlan 99
(Aruba620) (config-subif)#ip address [IP ADDRESS] [SUBNET MASK]
2) Default gateway
(Aruba620) (config) #ip default-gateway [IP ADDRESS]
3) If you need to change the management VLAN of the controller to use VLAN 99:
(Aruba620) (config) #controller-ip vlan 99
If you need to delete any of the existing IPs (such as default gateway) use the #no statement before
(Aruba620) (config) #no ip default-gateway 1.1.1.1