WARNING! By factory resetting your phone you will lose all personal data stored on the internal memory, including downloaded applications, images, contacts, ringtones and so on. All the settings will be restored to factory values.

NOTE: To learn how to back up and restore your data before master resetting the phone, follow this link for a full guide.

Master Reset via Settings:

  1. Tap "Apps" on the home screen
  2. Go to "Settings" and scroll to "Personal"
  3. Tap "Backup and reset"
  4. Optionally, enable "Back up my data" and "Automatic Restore"
  5. Tap "Factory data reset"
  6. Tap "Reset device" and assuming that your phone is protected by a PIN / password, enter it and tap "Continue"
  7. Tap "Delete all" to confirm

Master Reset via Recovery (Hardware Keys):

NOTE: In case you are unable to master reset your phone using the method above, you can also try factory resetting it via the recovery menu (through a combination of hardware key presses). To do so:

  1. Turn off your smartphone
  2. Press and hold the "Volume Up", "Home" and "Power" buttons simultaneously
  3. Once the phone turns on and shows the "Samsung" logo, release the "Power" button
  4. At the "Android" logo, release "Volume Up" and "Home" too
  5. From the recovery menu press "Volume down" to navigate to and highlight "wipe data / factory reset"
  6. Press "Power" to select the highlighted option
  7. Press "Volume down" to highlight "Yes -- delete all user data"
  8. Press "Power"
  9. Wait for "Reboot system now" to appear and press "Power" one last time to restart you phone

See More: Samsung Galaxy S6 Active: Factory Reset via Settings or Recovery (hardware keys)