Here's how to find the latest ViperOneM8 -
http://venomroms.com/htc-one-m8/
And the latest version has a link to the firmware requirement. (Ignore statement "rom is not ready, the page was written last October.)
There are three ways to update firmware.
1. Unroot, return to stock (including the recovery), relock bootloader, take OTAs until current, unlock bootloader, reinstall TWRP, install rom.
2. Lock bootloader, run an RUU if the *exact* one needed exists (and good luck on that!), unlock bootloader, reinstall TWRP, install rom.
3A. Have s-off and do an RUU-type flash of just the firmware. Usually always requires the supercid mod (because gsm radio firmware is the same regardless of carrier, but the firmware payloads identify for the carrier that the dev snagged them from - so supercid lies to the fastboot update process and says, yes I am your phone, so the firmware will flash).
3B. Have s-off on Sprint - get the firmware from Captain Throwback, place on sd card, flash by booting into fastboot, no pc required.
3C. Have s-off on Verizon - I'm the wrong guy to ask.