"Expert" HTC 10 owners in Europe can now flash Android 7.0 on their phone
The process of flashing the firmware will essentially delete all of the information and data on your HTC 10. Obviously, you should back up the data and information on the device before you go ahead and begin. A USB cable connects the phone to your computer and you should make sure that your HTC 10 has at least 30% battery life remaining. We suggest that you visit HTC's information page before you start, which can be found by clicking on the sourcelink.
If you've never attempted anything like this before, we would recommend that you wait for the Android 7.0 update to resume. One mistake and you could end up with a bricked flagship.
source: HTC via AndroidAuthority