Purchase additional licences for WatchGuard System Manager
WatchGuard appliances can be managed in a variety of ways including WatchGuard System Manager, a software management suite. Each appliance ships licensed to manage a limited number of additional appliances. A WatchGuard WSM licence allows you to centrally manage multiple devices, WatchGuard System Manager can be used to manage any Firebox, XTM or XTMv appliance.
Watchguard System Manager