The latest watchOS 2.2 beta can be downloaded through the dedicated Apple Watch app on an iPhone running the iOS 9.3 beta by going to General --> Software update. To install the update, the Apple Watch must have 50 percent battery, it must be placed on the Apple Watch charger, and it must be in range of the iPhone.
watchOS 2.2, along with iOS 9.3, introduces support for pairing multiple Apple Watches with a single iPhone. Both updates are required, with each watch running watchOS 2.2 and each iPhone running iOS 9.3. watchOS 2.2 also includes a revamped look for the built-in Maps app on the Apple Watch with access to the Nearby feature first introduced with iOS 9 and new buttons for quickly accessing directions to home and work.
There were no other obvious outward-facing changes introduced in the first five watchOS 2.2 betas aside from the changes to the Maps app, but the update undoubtedly includes under-the-hood performance updates and bug fixes to address issues that have been discovered since the release of watchOS 2.1. WatchOS 2.2 is expected to debut in the spring, perhaps at Apple's rumored March 21 event.