Apple has released Apple TV Software Update 5.1 (http://macte.ch/whMvI). It adds shared photo streams, iTunes account switching, and new AirPlay options.
To update your Apple TV to the current software version:
° Select Settings > General > Update Software. Apple TV checks to see if an update is available and a download message should appear if an update is available.
° Click Download and Install to start the download process (or Download Now on an Apple TV 1st generation with Apple TV software 1.x).
Do not disconnect your Apple TV during the update process. The Apple TV status light may flash slowly during the update and restart process; this is expected behavior.
On an Apple TV (1st generation) with software version 1.x: When the update has finished downloading, an Update Now message should appear. To start the update process, click Update Now.
During the update process, your Apple TV may restart, then display one or two Apple logos and status bars, depending on which Apple TV you have.