If you forgot your screen lock combination follow these steps.
Warning!All data will be lost!
1.Power off your phone
2.Press together volume up + volume down +home button + power button
3.Release your fingers of the phone when Samsung logo appear
4.Choose with volume buttons "wipe data/factory reset" and select it with power button
5.Choose "yes" with volume buttons and select it with power button
6.Wait untiil format is complete