HTC One M9 User Manual page 235

Resetting HTC One M9 (Hard reset)
If HTC One M9 has a persistent problem that cannot be solved, you can perform a
factory reset (also called a hard reset or master reset). A factory reset reverts the phone
back to its initial state—the state before you turned on the phone for the first time.
Factory reset will remove all data on your phone storage, including apps
you've downloaded and installed, your accounts, your files, as well as system
and app data and settings. Be sure to back up any data and files you want to
keep before you do a factory reset.
1. From the Home screen, tap
2. Tap Reset phone.
To also delete media and other data from your storage card, select Erase SD
card.
3. Tap OK.
A factory reset may not permanently erase all data from your phone,
including personal information.
> Settings > Backup & reset.
Sync, backup, and reset 235