Google releases Lollipop 5.0.2 factory image for Nexus 7 2013 Wifi

So far there’s not many devices that have gotten 5.0.2

Simply a factory image that you download to computer and flash to your tablet with fastboot.

https://developers.google.com/android/nexus/images#razor

You have installation instructions further up the page, and the tablet needs to be unlocked for installation to work.