Apple has today released an update to the Apple TV, bringing the software version to 4.4.2. If you haven’t previously updated, this will add the AirPlay Mirroring, Photo Stream, NHL, WSJ Live and Trailers apps. It is likely that this is a maintenance release that fixes bugs, as was the 4.4.1 release.
You can download the update by visiting Settings>General>Update Software on your Apple TV or by downloading it directly here and updating via iTunes.
Note that Apple suggests that you reset your Apple TV before updating:
Go to Settings -> General -> Reset -> Reset All Settings, prior to updating. If you apply the software update without resetting all settings first, the updater will reset the settings for you. Once the Apple TV has been reset, you can then successfully update to the latest software by going to Settings -> General -> Update Software.