First, obligatory words of caution:
- Do not try this on your daily driver. Since it is a beta, it has performance and stability issues. I have been using it since it was released and the experience has been rocky, to say the least.
- Make sure to backup your data using iTunes so you can easily restore in case of any issue.
- Ensure that your iPhone or iPad is sufficiently charged.
- In case you do not want to try out this method, you can wait for the public beta which should begin in July. This is a safer route since public betas are generally more stable than developer betas.
Now that the warnings are out of the way and assuming that you know what you are doing, here is the method. Note that this will not perform a clean install. It will upgrade from your existing iOS version.
The trick to installing iOS 10 beta is to use a configuration profile, which can be found through a quick search on Google. Once you have the link to the configuration profile, open it in Safari on your iPhone or iPad, download it and install it. You would have to input your passcode to install it. Once done, open up Settings > General > Software Update on your iPhone and iPad and wait for the beta update to show up. You should be able to download and install it to your iOS device now.
There are tons of features to try out in iOS 10. Messages, notifications, 3D Touch on home screen/control center icons/folder icons and so on. We are working on our detailed preview of the beta and will be sharing our impressions over the next few days.
You can also update your Apple Watch to watchOS 3 without an Apple Developer account.
P.S. if you are looking for the iOS 10 beta wallpaper, download it from here.