The Asus Transformer AiO is a unique device, with a Windows computer combined with an Android tablet. The device features a detachable 18.4 inch touch display with a 1920 by 1080 pixel resolution which is shared with both the PC and the tablet.Now the Android component is set to receive the Android 4.2.1 update which will bring one of the best features of Android 4.2 Jelly Bean - multi-user support.
Multi-user support is almost essential for a machine like this, making it more family friendly than it was with Android 4.1 Jelly Bean on board. Users can now use their personal logins on Windows and do the same when they are using the device in its tablet form factor.
You should receive a notification when the update is available for your device. But if you havnt, you can manually check for by heading to Settings > About tablet > System updates.
source - Android Police