While the international HTC One received the Android 4.3 update few days back beginning from Taiwan, it is now time for the users in the west to experience Android 4.3 on their HTC One. Users on the AT&T network using HTC One can now update their OS to Android 4.3. If you don’t get a notification for a software update, you can update the device by going to Settings>About phone and check for software updates. The build number for this update is 3.17.502.3.
While most of you must receive the update Over The Air (OTA), there might be a few who don’t get it that way probably because they have flashed a ROM that is not based on HTC’s stock firmware. In case you have made your device S-OFF, you will not receive the update but there is a workaround for that.
Make sure you know how to run the RUU zip file and perform the ROM update on the phone. The above link to download the RUU from htc.com also explains how to perform the ROM update. S-OFF users can perform the update by flashing the zip file on their device.