As in a phone from an American carrier like AT&T, T-Mobile US etc.
This have changed a bit since my last post about it, so I will just focus on the two ways to get updates. And this assumes that you haven’t changed your phones in ways that prevents this from working.
Simply go to the Rom downloads page, and just download what you need. AT&T One M7 is no longer available on that page.
There you can actually update or phone via HTC Sync Manager, I assume that it’s done in a similar way as the rom downloads. Not sure just what phones this work on, but this is the help-text from the Verizon One Max support
If you already have HTC Sync Manager open, you can manually check for software updates for your phones.
On the Window’s system tray, right-click on the HTC Sync Manager icon, and choose Check for firmware updates.
If an update is found, connect your phone to your computer, and click Update now.
Start the software update process. For more information, see below.
If there is an available update, you can upgrade your phone’s software through HTC Sync Manager.Important: Make sure that there is enough power on your phone before starting the software update. The download takes about 20 minutes (depending on the speed of your internet connection) and the software update takes about 15 minutes.
Connect your phone to your computer. If your phone has an available update, a notification displays.
On the Software Upgrade Assistant page, select your phone from the list, and then click Upgrade.Your computer downloads the update. After the download is completed, the software update process starts immediately.Note: During the update, the phone will restart a few times.
A message appears when the update has been completed. Click Close to return to HTC Sync Manager.