WARNING! If you factory reset your phone, all data stored on the device’s internal memory will be lost, including ringtones, apps, contacts, downloads images and so on. Furthermore, all settings will be restored to default values.

NOTE: Before master resetting your phone, you can visit this thread for instructions on backing up data, and this thread for a guide on restoring data.

Master Reset via Settings:

  1. Tap “Apps” on the home screen
  2. Open “Settings”
  3. Scroll to “Personal” and tap “Backup & reset”
  4. Enable or disable “Backup my data” and “Automatic restore”
  5. Tap “Reset phone”
  6. In case your phone is lock screen-protected, enter the necessary security credentials to proceed
  7. Optionally enable “Erase SD Card” to format the external storage too
  8. Tap “OK”
  9. At the “Warning” pop-up, tap “OK”
  10. Tap “OK” one more time to confirm and reset the device

Factory Reset via Recovery (Hardware Keys):

NOTE: If you are unable to reset the phone via Settings as described above, you can try factory resetting it via Recovery, by performing a combination of button presses. To do so:

  1. Turn off the phone
  2. Press and hold “Volume Down”
  3. Press and hold “Power” until the phone vibrates, then release the button
  4. Once the phone boots in “hTC download mode”, release “Volume Down” too
  5. Press “Volume Down” repeatedly to navigate the menu and highlight “reboot to bootloader”
  6. Press “Power” to select the highlighted option
  7. From the next menu, press “Volume down” to highlight “Boot to recovery mode”
  8. Press “Power”
  9. When the phone shows a black screen with a red exclamation mark, hold “Power” and press & release “Volume Up”
  10. Release the “Power” key in the “Android system recovery” menu
  11. From here, press “Volume down” repeatedly to highlight “wipe data / factory reset”
  12. Press “Power” to select the option
  13. Highlight “Yes – delete all user data” and press “Power”
  14. One the phone is reset, you will be prompted to “reboot system now”. Press “Power” to reboot the device

Check for Software Updates:

NOTE: After a factory reset you should verify if a new firmware update is available for download. To do this:

  1. Open the apps drawer
  2. Launch “Settings”
  3. Scroll to “Phone” and tap “About”
  4. Tap “Software information”
  5. Assuming that an update is available, follow the on-screen steps to apply it

See More: HTC One M9+ Supreme Camera: Factory Reset and Check for Firmware Updates