WARNING! When you master reset your phone, all personal data stored on the internal memory will be deleted, including apps, downloaded content, contacts, media files etc. Additionally, all settings will be restored to default.

NOTE: Before you factory reset your phone, you can visit this thread for instructions on how to back up data, and this thread for restoring data. You can also visit this thread for more backup and restore options locally or via HTC Backup.

Factory Reset via Settings:

  1. Open the apps drawer
  2. Go to “Settings”
  3. Scroll to “Personal” and tap “Backup & reset”
  4. Turn on or off “Backup my data” and “Automatic restore"
  5. Tap “Reset phone”
  6. If your phone is protected by a lock screen, enter the required password / PIN to proceed
  7. Optionally, enable “Erase SD Card” too
  8. Tap “OK”
  9. Read the “Warning” pop-up and tap “OK”
  10. Tap “OK” one last time to confirm and reset your phone

Factory Reset via Recovery:

NOTE: In case you are unable to reset your phone via Settings, you can try resetting it via Recovery instead. The Recovery menu can be accessed by performing a combination of button presses.

  1. Turn off the phone
  2. Press and hold “Volume down”
  3. Next, press & hold “Power”
  4. When the phone vibrates, release “Power”
  5. After the phone shows the “hTC download mode” menu, release “Volume Down” as well
  6. From the menu, press “Volume Down” repeatedly to highlight “reboot to bootloader”
  7. Press “Power” to select the highlighted option
  8. In the next menu, press “Volume down” to highlight “Boot to recovery mode”
  9. Press “Power”
  10. When the phone shows a red exclamation mark, press and hold “Power”, then press and release “Volume Up”
  11. When you reach the “Android system recovery” menu, release all buttons
  12. Press “Volume down” to navigate the recovery menu and highlight “wipe data / factory reset”
  13. Press “Power”
  14. Highlight “Yes – delete all user data”
  15. Press “Power”
  16. After the phone resets, make sure “reboot system now” is highlighted and press “Power”

Check for OS Updates:

NOTE: After you factory reset your phone, it’s recommended that you check for OS updates. To do this:

  1. Tap “Apps” on the home screen
  2. Scroll down to “Phone”
  3. Tap “About” > “Software information”
  4. If an update is available, follow the on-screen steps to download and apply it

See More: HTC One M9s: Factory Reset and Check for OS Updates