The update address issues where audio and video are occasionally missing when playing back certain content. A new audio output setting allows you to switch to 16-bit audio, for increased compatibility with some TVs and AV receivers. Fast-forwarding and rewinding of live events is improved, too.
Rounding out the updates are fixes for an issue with missing movie descriptions and another where YouTube subscription videos were not correctly sorted by date.
You can install the update on your Apple TV by navigating to Settings -> General -> Update Software and following the directions there.
The full update is available directly from Apple