Removing the rear alluminum case is the hardest part of repairing the internals of the HTC One. In many blogs/videos the backing is damaged so its worth buying a spare one for this repair just in case theres damage.

The unit I've got was already popped open.

A contributor found it easier and minimal damage to get into the case by prying inside the sim card slot area first and then working their way around with guitar picks.

Additional videos that might also help with this process:

http://youtu.be/qZFAsgjCunc

http://www.youtube.com/watch?v=cyrxa23Ow...

After you have removed the rear aluminum case for the first time and broken that adhesive, the back case will come on and off easily using the plastic pry tools