Return to stock or update to the latest version on your Nexus 7
Along with the Nexus 4, all versions of the Nexus 7 have also received Android 4.4 factory images. Even though the OTA update to KitKat hasn’t come to the Nexus 7 variants that have mobile data, all four variants of the smaller Nexus tablet have factory images available.
If you’re willing to put a little time into it you can use these to update your own tablet, or just download and have them at the ready should you ever need to return to stock.
More: Nexus 7 2013 Forums | Nexus 7 2012 Forums
Source: Google Developers