its easy you can just restore the phone to the Factory defaults or
doing a Device Format


Steps to format your Galaxy Phone

1- shutdown the device first (Switch the Device off)

2- press the Volume UP Button and Power Button and Home Button in the same time
for just a Four seconds and when the Samsung Logo appear
leave the Power Button and still pressing on the Volume up Button

3- after that the recovery screen will appear and then chose (wipe Data/factory reset)
and then press Home Button and the Device will be formatted and
factory settings will be loaded  successfully