As in a phone from an American carrier like AT&T, T-Mobile US etc.
If you got an AT&T etc phone you might have noticed that if you’re outside the USA, that OTA updates just doesn’t work. So, be VERY aware of this if you indeed get an American carrier phone. As they ARE different from the rest of the world. 4G LTE might now work, and on. So, ALWAYS know what you buy.
Simply go to the Rom downloads page, and just download what you need. AT&T One M7 is no longer available on that page. And don’t attempt doing this if there’s been changes to the bootloader etc.
There you can actually update the phone via HTC Sync Manager. Follow this how to update your Verizon phone.