To install the beta, you'll need the proper configuration profile, which can be obtained through the Apple Developer Center. Once the profile is in place, the watchOS 5 beta can be downloaded using the dedicated Apple Watch app on the iPhone by going to General --> Software Update.
To update, the Apple Watch needs to have 50 percent battery, it must be placed on an Apple Watch charger, and it has to be in range of the iPhone. It would be wise to install the beta on a secondary device instead of a primary device given that this is an early version of the watchOS 5 software that still has bugs to be worked out.
watchOS 5 is a major update to watchOS, introducing Activity Competitions so you can compete on workouts with friends, Walkie-Talkie with push-to-talk functionality for quickly communicating with the people you talk to most, and auto workout detection to make it easier to start and stop workouts if you forget.
Other new features include an improved Siri watch face with support for third-party apps through Siri Shortcuts, a dedicated Apple Podcasts app, new Workout types that include Yoga and Hiking, new features for runners, WebKit support for viewing some web content on Apple Watch, and enhanced notifications, which will make notifications on the Apple Watch interactive.
Early software betas often introduce new functionality, so we'll update this post if anything new is found in the fourth beta of watchOS 5.
watchOS 5 is only available to developers and will not be provided to public beta testers (because there's no way to downgrade Apple Watch software), so non-developers will need to wait until the software is officially released in the fall to try it out.
The watchOS 5 update runs on all Series 1, Series 2, and Series 3 Apple Watch models, but it is not available for the first-generation "Series 0" Apple Watch models.
What's new in beta 4: The Walkie-Talkie icon on the Apple Watch face is no longer persistent. It will now be displayed briefly when lifting your wrist before fading away. Walkie-Talkie also appears to obey your Do Not Disturb settings, so other Walkie-Talkie users are not able to contact you when Do Not Disturb is turned on.