If you have never flashed a factory image before, you might want to wait for the OTA update to hit your device instead. As for the content of the update, it most likely contains bug fixes and performance enhancements after the initial dissemination of the Android N Developer Preview earlier this month. Google surprised everyone by making the Developer Preview available to recent Nexus handsets months before the expected release at Google I/O in May. The final version of the OS will be launched later this year, most likely during the third quarter.
If you need instructions on how to flash the new factory images to your Nexus phone, you can find them along with the appropriate links by clicking on the sourcelink. To receive automatic OTA updates of the Android N Developer Preview instead, you must enroll to the Android Beta Program. To do that, you also need to click on the sourcelink.
source: AndroidDevelopers via DroidLife