Using a phone that hasn't been updated is like playing NBA 2K10 in 2013. Everything works fine, but you're missing all those new features and current rosters.
So, when using your Samsung Galaxy S3, try to update as soon as possible to stay current with the Android software. Updating your phone is a fairly straightforward process.
First, you'll want to make sure you have an account set up on your device. Go to Settings -> Accounts & Sync -> Add account and choose what option works best for you.
You will then be prompted to set up an account, which requires an email address and password.
If you already have an account, you'll see it listed in the menu and you can chose to update or sync it.
Once your account is enabled, you can proceed to Settings -> About Device -> Software Update -> Update. If no update is immediately available, press Check for Updates instead to see if one exists.
You may download updates without an account, but some updates may ask prompt you to do so.
It will check to see if there are any updates available. If there are it will inform you, and then begin to download.
You will want to be on a Wi-Fi network and have your device plugged in. Depending on the size of the update, it could take a while.
When the download is complete you will be notified and must restart your device.
Pretty easy. And don't be surprised if there aren't any updates available for your GS3. It took me forever to get the official 4.1.2 from 4.1.1 on my AT&T version.
Have questions or issues? Leave them in the comments section.