Things that I recommend you to do before following the hard reset guide below.
Backup your Android data.
Have a battery life, at least 80% power.
How to factory reset / hard reset Samsung Galaxy Mega 6.3 GT-I9200
- Take off your SIM or Memory Card, then power off your Samsung Galaxy Mega 6.3 GT-I9200.
- Take your device battery out, wait for about 10 seconds, then insert it again.
- Now hold and press these buttons together: Volume Up + Home, and then press Power.
- Keep holding those buttons, till your see the Samsung Logo shows itself, then release all the buttons.
- Now wait till you are entering Factory reset / System Recovery menu.
- Now use Volume Down key to scroll and choose this option Wipe Data / Factory Reset.
- To confirm the step you need to use Home button.
- Now choose "Yes -- delete all user data" using Volume Down key.
- Now to confirm the step use Home button.
- Once you have performed the hard reset, choose this option: Reboot System Now, after it's chosen then use Home button to confirm it.
- Your phone will be booting now, once it's ON again then it's ready to use.