WARNING! When you master reset a phone, all of your personal data stored on the device’s internal memory will be lost, including ringtones, downloaded content, media files, contacts, apps etc. Furthermore, all the settings will be restored to factory values.

NOTE: Before you reset the phone, you can visit this thread for a guide on how to back up data, and this thread for instructions on restoring data from your backups on the Galaxy A9.

Master Reset via Settings:

  1. Tap “Apps” on the home screen
  2. Launch “Settings”
  3. Under “Personal”, tap “Backup and reset”
  4. Optionally, you can enable or disable “Back up my data” and “Restore”
  5. Tap “Factory data reset” > “Reset device”
  6. In case your phone is protected by a lock screen, enter the PIN / password / pattern and proceed
  7. Tap “Continue” > “Delete all”

Master Reset via Recovery:

NOTE: In case you are unable to reset the phone using the method above, alternatively you can try resetting it via Recovery. The recovery menu can be accessed after performing a combination of button presses, as follows:

  1. First, make sure the phone is turned off
  2. Next, press and hold “Power”, “Home”, and “Volume Up” at the same time
  3. When the “Samsung” logo appears, release “Power”
  4. When the “Android” logo pops-up, release all other hardware keys
  5. After a few moments you should see the “Android system recovery” menu
  6. From the menu, press “Volume down” repeatedly to navigate to “Wipe data / factory reset”
  7. Press “Power” to select the highlighted option
  8. Use “Volume Down” to highlight “Yes – delete all user data”
  9. Press “Power”
  10. After your phone has been reset, “Reboot system now” should be highlighted. Press “Power” one last time and wait for your phone to reboot

Check for OS Updates:

NOTE: After factory resetting your phone, you should verify if newer software updates are available for download. To do this:

  1. Tap “Apps” on the home screen
  2. Open “Settings”
  3. Scroll to “System” and tap “About device”
  4. Verify if new updates are available. If there are, follow the on-screen prompts to download and apply it

See More: Samsung Galaxy A9: Master Reset the Phone and Update the OS