Recently, we posted an installation guide on how to install Android M on Nexus devices, and most of our users have already upgraded their device to Android M, but some of them complained about bug errors in the Android M Preview version. Though the Android M is a better operating system compared to the Android lollipop, but I encourage you downgrade to android lollipop if you are disturbed much by those bug errors.
» Once you run any of the above file (depending on the type of PC you use), the flashing process would begin, and it might take few minutes.
Installation Guide to Downgrade from Android M to Android 5.1.1 Lollipop on Nexus
» First off, download the Android lollipop Image from the link provided below, then extract to the desktop menu of your computer.
» Now, enable USB debugging on your device and connect your device to PC via USB cable.
» After that, boot your device to bootloader mode by pressing Power and Volume Down buttons together.
» Once you're in bootloader mode, then go to the Android M folder that you extracted in the first step, then run the file named;
For Windows PC - flash-all.batFor Linux- flash-all.sh
» Once you run any of the above file (depending on the type of PC you use), the flashing process would begin, and it might take few minutes.
Once the process is completed, your Nexus device would be restarted automatically.