Step-by-step procedure. See below:-
Step 1: Do turn off power of your mobile device, press and hold Volume Up key or Home key then press Power key until you will see Samsung logo on the screen.

Step 2: Select with volume down key buttons "Wipe Data/Factory Reset" and press power button to confirm.

Step 3: Use the volume down key buttons again to select “Yes--delete all user data” and press power button to confirm.

Step 4: Wait until format is complete and press Power key to confirm “Reboot System” option.

Step 5: Now the phone will reboots, Wait until the phone restarts.

http://tarunmittal5477272.buzznet.com/user/journal/17368178/factory-reset-hard-reset-samsung/