you may not be able to get an ota (over-the-air) because it is delivered over at&t's network which you may not have access to. You can, however, do a 2-step manual update to the latest version which is ver. 4.3 following the instructions below ....
1) go to the first page in the thread below ...
http://xdaforums.com/showthread.php?t=2387423
2) download the 2 zip files under update412.zip and update43.zip respectively to your computer
3) copy the zip files to a good quality (micro) sd card
4) place the card in your phone and boot to recovery mode by simultaneously holding down the volume up, home and power buttons
5) hold the buttons until you see a blue message flash across the screen. Then release the power button but continue to hold the volume up and home button until you see the android image appear. Then release the buttons
6) use the volume up/down key to scroll to <mount from external storage> and the power button to select
7) navigate to the first zip file (update412.zip) and install. Wait for installation to finish and your phone to reboot.
8) complete set up. Check your phone settings. Then power off and reboot to recovery again.
9) repeat the process for the second update file.
Please let me know if this works for you.