After the iOS 6 public release, Apple have released a major update to Apple TV 2G and 3G, labeling the version number 5.1 and build number 10A406e. It was back in June (5th of June to be exact), the previous update (version 5.0.2) for Apple TV came in.
The update of course brings in some new handy features including options for photo stream sharing, AirPlay, switching between iTunes accounts, subtitle, trailers, screen savers etc. You can have a look at the official change log posted here about the iOS 5.1 update for Apple TV 2G/3G.
How to update your Apple TV to iOS 5.1
How to update via automatic updates
1. Navigate to Settings -> General -> Update Software.
2. Once it is shown that the update is available, choose ‘Download and Install’ option and wait till it is over.
How to update using ipsw file
1. Download the ipsw file from below (it’ll be a dmg file. Just change the extension to ipsw).
2. Connect your device to the computer.
3. Open iTunes and choose your Apple TV from the left panel.
4. Click on ‘Restore’ button while holding the shift key (Windows) or option key (Mac).
5. Point to the iOS 5.1 ipsw file and you are done!
Download iOS 5.1 IPSW for Apple TV 2G from here
Download iOS 5.1 IPSW for Apple TV 3G from here