No way to get At&t update if outside US and not on At&t. ROM flashing is the way.
if you are not in US and not on At&t network currently . I checked there are no proper OTA files for the AT&T to update via OTA method if you are stuck on 4.1 ( 1.25. xxxx) . Via OTA files user data is preserved. No need to re-setup your device.
So you can't just go without flashing the phone and re-setup of old apps and stuff is required.
Now that you have to flash the phone its so much better to leave At&T builds. They have the highest amount of junk ( bloatware) in their builds. At&t phone book app i hate you.
So, do one step more and convert your phone to a generic version. US developer version is the best. Updates are faster and directly from HTC. And Rom has no issues.
That one step more is changing your CID and MEID in fastboot menu. ( it requires a S-off , and S-off might require a root. Root might require a TWRP recovery and SU binary steps ) .
If you on 1.44 Hboot the story is easy , just s-off via revone and unlock bootloader( i guess not needed !) and then flash a JB (4.3) binary first and then update to KK. Don't jump to KK directly with RUU.exe method . It fails with image error 158. I spent 5 hours figuring why this error !!!
Also can be converted to any other edition by changing the respective CID and MEID. Later make sure the CID is correct to receive the future OTA updates.
PS : T-Mobile is so much better in terms of pushing OTA. I had a m7 t-mobile SIM unlocked outside US. Never had a issue for any OTA. All were pushed on time.
Very unprofessional of At&t, that they want only their 'active' At&t members only to get the updates.
IF they see that the update binary is already same for all and is ready, its just server bandwidth they need, to extend OTA to non-At&t subscribers using an At&t phone.