Oye, Good News here! If you have been waiting to update your Samsung Galaxy S III (AT&T) to Android 4.1 Jelly Bean, then the wait it over. I just updated my phone and here are the steps that I followed to update my phone.
Step 1: Start here
Step 2: From this Link, download and install Samsung Kies. Looks like there is no over-the-air update for this version
Step 3: Connect your phone to your PC
Once Kies is installed, connect your galaxy S III to the PC. Kies prompted me for an update of the Kies software, which I accepted.
I hit OK for the below prompt:
Step 4: Go head and update
That should do it.
Here are the new features that comes with Android 4.1 Jelly Bean