Is there any way to update software on an AT&T branded HTC ONE M7 in the UK?

[AC Question]

Phone is HTC ONE M7 branded AT&T mobile unlocked and on the O2 (Giffgaff) network.
Current software info:
Android 4.3
HTC Sense 5.0
S/W No. 3.17.502.3
In Settings there is an AT&T Software Update option which, as it cannot find the AT&T / Verizon network has never found an available update.
HTC refer me to AT&T and vice versa.
Can anybody tell me if I will be able to update or will I ultimately have to look into the mind-blowing mysteries of rooting?
Cheers.

 

[Rukbat]

Go to AT&T HTC One - XDA Forums and see if there's a thread for a 4.4.2 or 4.4.4 AT&T update. (You probably want to wait a while to update to Lollipop - it's still in the "which bugs haven't we found yet" stage.) There will be instructions in the thread, or you can post a question in the thread if you can't figure out how to do it.

BTW, HTC doesn't void the warranty if you root (they're the only company that doesn't), and Kingo will root 4.3 effortlessly. (Not that you want to if you want to update - you can't update a rooted phone, and you root the ROM, so you'd have to root after updating. Just get familiar with that forum and you'll become a lot more familiar with your phone.)