The Android 6 Marshmallow ROM for HTC One V is available for download. Since this is an early port, not every thing is working and this includes camera, flashlight, adoptable storage and headset microphone do not work in calls. To install it, you will need latest version of TWRP.
After that, download the ROM from here and flash it by downloading it to storage card and flash it from recovery. We also suggest install gapps since they are not part of the ROM. This too can be installed from recovery.
Installation instructions for downloading and installing Android 6 Marshmallow ROM for HTC One V
Windows users: Download and install this tool. Mac OS X users: Download Android SDK and get the platform tools. Linux users: Get adb and fastboot using your package manager.
Download the rom and copy it to sd card
Boot into bootloader and flash this recovery
Boot into recovery
Wipe data/factory reset
Wipe cache partition
Select install zip from sd card.
Install the rom-zip.
Extract boot.img inside the roms zip-file.
Boot into bootloader and flash the kernel:
fastboot flash boot boot.img
Reboot your device, it will take about 10 to 20 min to boot.