After announcing the rollout of the Android 5.1.0 update, Google has already posted the factory images for some of the Nexus devices.
The latest version of Lollipop has the build number LMY47D, and is currently only available for the Nexus 5, Nexus 7 (2012 WiFi) and Nexus 10.
Do not try to flash the image on any other Nexus devices, until they are officially released by Google.
Download Android 5.1.0 Lollipop LMY47D factory image for the
Nexus 5 (Hammerhead) md5: 021fa0ed4946e0c7e70e39da301e5a34
Nexus 7 2012 WiFi (Nakasi) md5: 35b23c78db9a7eb043a0b1a76ee0874a
Nexus 10 (Mantaray) md5: 43a649017cc8a186d737d3288346d092
You can follow the steps given in our previous guide to flash Android 5.1.0 on your supported Nexus device. Flashing a factory image will erase all data on your device, so make sure to take a backup of your data before flashing the new firmware.
Always check the MD5 hash value of the downloaded file before flashing it. You can do so by using the free HashTab app for Windows explorer.