So I have rooted my Samsung Galaxy S3 I9300 and now want to un-root it. I want it back to stock, how can I do this?
For unrooting you should always see videos
Unroot the Galaxy SIII (for stock updates/warranty)
uninstall su app by chainfire and then reboot ur device
Uninstalling Super User does not un-root a device, only stops one from granting applications root access. Flashing the stock ROM and stock recovery would completely get the phone back to a stock non-rooted device. There also is a way to reset the trip counter so that the phone does not look like it was tampered with at all. Many of the recommended links will help, especially xda-developers.
I think this site will help you to un-root your Samsung Galaxy S3 I9300
Visit here and follow the steps