Well today I ran into that exact problem, the existent management VLAN was 16 so obviously having the switch's management interface on VLAN 1 was no good.
After a fair bit of searching google and the Ubiquiti Networks forums I was beginning to lose hope! , it seemed no one knew how to change it, there was even a feature request post asking for the very feature I was now in need of.
However I persevered and dug through both the CLI of the switch and the cloud key management controller interface until ....... I found the needed option, tucked away under the services heading of the configuration tab of the switch.
so here is an image of it
I hope this helps some of you out in the future.