It will remove all the data ,contacts and apps that you installed
Power off your phone.
Then press and hold together Home button + Volume Up button + Power button until the phone vibrates.
After a few seconds you will see little man Android and after that menu recovery.
In the menu choose with Volume buttons "wipe data/factory reset" and select it with Power button.
Next select "yes".
After this operation select "reboot".
Samsung Galaxy Core I8260 Restore Factory Hard Reset Format Phone.So lets start the Samsung Galaxy Core I8260 Restore Factory, Samsung Galaxy Core I8260 Hard Reset.Turn Off the mobile phone for few mints.Samsung Galaxy Core I8260 Remove Pattern Lock.
Restore Hard reset will set your phone in origional factorry settings. It will remove all the data and apps that you installed. Your contacts will be removed and you have to add them again.