One canlog into their Gmail account and move down to the list of eligible devices and choose Unenroll Device. Keep in mind that your device will need to do a factory reset after that.
There were new features introduced by the Developer Preview and they include Multi-window, improved Doze mode, bundled notifications along with the option to reply to incoming stuff coming from notification.
Bug fixes were introduced by the second DP, specifically for multi-window and various other issues were reported through the public issue tracker as well. At the same time, there are new emoji that are more human-resembling and there are launcher shortcuts along with a new 3D rendering API named Vulkan.
The latest reports from Google have already reported that Google is already working had on a couple of new handsets which are undoubtedly the successors of Nexus 6P and Nexus 5X. Keep in mind that Huawei and LG will be making them.
Reports indicate that HTC was supposedly hired by Google which is the same company that made the iconic Nexus One. Newer reports indicate that Google may further partner up with HTC for the 2016 Nexus handsets and reports indicate that these two devices are presently under development.
Stay tuned for more updates on Android N!