Google releases a developer preview version of its latest android os Android N. Although, there is no confirmation about what N stands for. The beta version of the latest android os is not intended for consumers for regular use, developers can download it for their testing and bug fixing purpose.
Currently you cannot install Android N on all phones. Only the newer Nexus devices like Nexus 5X, Nexus 6P, Nexus 6, Nexus Player or Nexus 9 and the tablet Pixel C are compatible with the preview version. The developer preview is only available in the format of factory images and you can download it for the above devices. 
As its a developer preview version, its not recommended for regular use. You may face bugs when you use, I recommend you to take a full backup of your android before installing Android N preview version.
How to Install Android N developer preview on Nexus 6p, 5x, 6, 9 via Factory Image
Install latest Android Studio Preview on your system, this helps to connect Android device via Micro-USB and flashing it. You can check this post to know about how to use android Studio Preview.
Then here are the steps you need to follow.
1. First Download the factory image for your android device.
2. Go to Settings > Developer options and tick USB debugging.
3. Extract the images and save on your computer.
4. Connect your device to your computer over USB.
5. Start the device in fastboot mode.
Using the ADB tool, boot into fastboot mode: When device powered on, execute the following in the command terminal: adb reboot bootloader. You you will get access to boot loader of your android device.
6. Navigate to unzipped system image directory.
7. Execute “flash-all.bat”, which should unzipped image files and install the necessary bootloader, baseband firmware(s), and operating system. It may take several minutes and reboot many times. After that Android N Developer Preview will be installed on your Device.
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Another way you can download latest Android N Developer Preview is via OTA Update. Check this tutorial to know about how to install Android N via OTA update here.
Source: Gadgets.ndtv.com
