Apple has released Apple TV TV Software Update 4.2.1 (http://support.apple.com/kb/HT4448), an update for the company’s streaming only version of the Apple TV.
The update addresses issues that may cause the screen to flicker or display incorrect color on some older TVs. It also addresses an issue where Apple TV may not wake up from sleep and an issue where audio may not be heard on some TV models after switching from another input. Apple TV Software Update 4.2.1 includes stability and performance fixes for Apple TV.
To update your Apple TV to the current software version:
Select Settings > General using your Apple Remote.
Click Update Software. At this time your 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).
Important: Do not disconnect your Apple TV during the update process. An Apple TV (1st generation) may flash an amber light; 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.