How to install Android N Developer Preview OTA: Video Guide
Android N Developer Preview OTA Update Page: Android Beta Program OR Alt Link
List of Compatible Devices, on which Android N Developer Preview can be installed: Nexus 6P, Nexus 5x, Nexus 6, Nexus 9, Nexus 9G, Nexus Player, Pixel C & General Mobile 4G
BACKUP DATA before proceeding. The OTA rollback will WIPE ALL DATA
If you updated to Android N Developer Preview OTA (over the air) on you compatible device & want to roll back to the latest stable Marshmallow build, just open google chrome on your device & go to either g.co/androidbeta OR google.com/android/beta. You will find a list of your devices enrolled for the android beta program, UNENROLL DEVICE will be written next to your already enrolled device. Simply click on Unenroll Device, confirm by clicking on LEAVE BETA & you can go to Settings-About Phone-System Update to start downloading the latest public Marshmallow Build. Once the download completes, follow the prompt to RESTART & INSTALL marshmallow on your device. Takes around 5 minutes. Phone restarts a couple of times. You get a fresh & clean install, all data gets a wipe. Do back up your data before starting the whole process.
Thanks a lot for viewing the post. Share your feedback in the comments section, it's invaluable.
Keep it simple stupid.