One week ago, Apple released watchOS 5 Beta 1 to developers at WWDC. Two days later, after several reports of bricked devices, Apple pulled the update. Today, it's available to download for developers.
If you aren't a developer, but would like to test watchOS 5, you can install a profile to get developer updates. We recommend using this profile. You can directly install it on your Apple Watch, without using a computer (of course, you need your iPhone).
watchOS 5 is the biggest watchOS update this year, and will probably be released to everyone this September/October. It was announced at WWDC18, one week ago. Read our article summarizing the whole WWDC-event here.