Update Nexus 7 to Android 4.3 manually without loosing data

Sometimes one has modified some system files and OTA is failing due to those modifications. The easiest way in that case would be to do the update manually by using the factory image. Unfortunately applying the factory image directly does a factory reset, so all data will be lost, but knowing the principles behind, you can go to the lastest Androis version without loosing your data.

Get the factory image from Google and extract the following files from it:

• bootloader-grouper-4.23.img
• boot.img
• system.img

If you have root and want to keep it, get
- UPDATE-SuperSU-v1.51.zip
and copy it to /sdcard and be sure, that you have a custom recovery installed on your device.

Then do a nandroid backup before starting (it's always better to have it) and then do a

fastboot flash bootloader bootloader-grouper-4.23.img
fastboot reboot-bootloader
fastboot flash boot boot.img
fastboot flash system system.img

reboot into recovery and flash UPDATE-SuperSU-v1.51.zip

Do a reboot system and, congrats, you should be on Android 4.3 without loosing any data.