Android Lollipop 5.1 Update Available For Select Nexus Devices
Android Lollipop 5.1 update was announced a couple of days ago and the official images are already being spotted in the wild. As of now, device images are only available for select Nexus device.
According to reports, the Lollipop 5.1 factory image is available for the 2012 Wi-Fi Nexus 7 (Nakasi), the GSM/LTE Nexus 5 (Hammerhead), and the Nexus 10 (Mantaray).
You can also check out the Google Developer page, that hosts information and download links of all the available Android images for Nexus devices.
A point worth noting is that these images need to be flashed manually, so you need to be very careful while updating your device ROM. You can also read the instructions for flashing the ROM, available at the Google Developer page.
In situation like this, applications such as Titanium Backup might come handy to take the back up of the device's data before proceeding.
Let us know how your adventure goes but be ware, in the world of rooting, things could often go awry.