[Q] Help me Unroot my GT-I9300!! (Im a Beginner) topic

hello...i followed a video to root my Galaxy S3 GT-I9300 and it automatically installed CWM Recovery Version 1.5 (non touch) and rooted my phone...now i want to go back to stock firmware ...but the problem is i purchased my phone from SIngapore and don't know which firmware i should download from Sammobile.com to unroot .....can i use any firmware (i.e. Firmware of any region for the unlocked GS3 GT-I9300) ...will it brick my phone.??? plz help....thanks in advance...