[Guide] Restore you phone to factory by Samsung Kies. Works on most Samsung units.
I see a lot of post asking :"How to restore phone to factory ?".I always do this way after i backup all i need and important data from my phone
I use Samsung Kies. They can be find HERE
1. Start Kies
2.Click Tools-> Firmware upgrade and initilazation
3.Type in model of your phone for example AT&T is : SGH-I747 ( all in capital letters) click OK. In some cases letter after number can be small. In example for Samsung Galaxy S3 Rogers you can try SGH-I747m.
4.Then type serial number off the stcker under battery also in capital letters click OK
5.There will be info about firmware click OK
6.Info about software version. Put your phone in download mode by pressing volume down key, home button and power button then connect to PC using orginal USB cable, click OK
7. Follow info on screen.
8. Phone will reboot by itself when all is done correctly.
Enjoy virgin phone llike from store. In some cases you will need to do OTA upgrade after all of this.
EDIT: I notice that sometimes you don't have to put phone in to download mode at all. Just connect and do step 2.
EDIT2 : If you update to 4.3 by OTA or if you install 4.3 bootloader on ATT S3 (I747) DO NOT USE THIS METOD. You will brick your phone.