Since you didn't mention the root status of the phone, you need to perform a factory reset of the phone.Here's how it's done:
Turn off the phone. Press Volume Up and Home buttons and, while keeping them pressed, press the Power button until the Samsung logo appears and blinks twice. Release the power button keeping the other two pressed until a list with options appears. Select "Wipe data/Factory Reset" using volume buttons and confirm with the Power button. After this procedure the phone will reboot and everything will come back to default condition.