HTC One M8 - Manual (Page 138)

Files such as your music, photos, videos, and documents can also be deleted from the
storage, if you chose to do so.
Be sure to back up any data and files you want to keep before you do a factory reset.
A factory reset may not permanently erase all data from your phone, including
personal information.
Performing a factory reset from settings
1. Go to Settings, and then tap Backup & reset.
2. Tap Reset phone.
3. If you want to delete media, documents, and other data from the phone storage,
select Erase all data.
To also delete media and other data from your storage card, select Erase SD
card.
4. Tap OK.
Performing a factory reset using hardware buttons
If you can’t turn HTC One on or access settings, you can still perform a factory reset
by using the hardware buttons on HTC One.
The Fast boot option in Settings > Power must not be selected.
1. Press and hold the VOLUME DOWN button, and then press and hold the
POWER button.
2. Wait for the screen with the three Android images to appear, and then release
the POWER and VOLUME DOWN buttons.
3. Press VOLUME DOWN to select FACTORY RESET, and then press the POWER
button.
138 Sync, backup, and reset