HTC One E8 - Manual (Page 130)

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.
To also delete media and other data from your storage card, select Erase SD card.
3. Tap OK.
130 Sync, backup, and reset