As I had my Nexus 7 3G 2012 tablet unlocked and rooted I didn’t get any official updates anymore.

But I still think the Nexus 7 tablet is the best tablet still I decided to get it a lollipop.

Be aware that everything will be removed from your device.
Your totally responsible for your actions, if you brick your device I can’t help you.
This description is not for beginners and I will not provide every detail of the processes.

Lets go.

  1. Download the google factory android image, look for “razorg” for Nexus 7 [2013] (Mobile), https://developers.google.com/android/nexus/images
  2. Follow the instructions at the top of that page to get the rom flashed, but don’t lock the bootloader again.
  3. Reboot your device to check that everything is working properly. (Be aware that first boot takes a while, be patience)
  4. If you get a image of a dead android with a red sign sticking out of its chest do a factory reset (instructions from google nexus support)
    While holding down the Power button, press and release the Volume Up button once.
    Press the Volume Down button twice to highlight “wipe data/factory reset,” then press the Power button to select it.
    Press the Volume Down button seven times to highlight “Yes – erase all user data,” then press the Power button to select it.
    After the reset is complete, select the option to reboot your device.
  5. Download the chainfire root tool and image: http://download.chainfire.eu/295/CF-Root/CF-Auto-Root/CF-Auto-Root-grouper-nakasi-nexus7.zip
  6. Unzip it and use fastboot to flash it
  7. sudo fastboot boot image/CF-Auto-Root-grouper-nakasi-nexus7.img
  8. It will reboot your device and performs it’s magic (placing su and pacthing the kernel)
  9. Be aware that it can take up to a minute before you see the red chanfire android and the patching starts.
  10. The device will reboot again (Mine did a second reboot just after booting the rom, not sure if that was intended)
  11. The device will boot into lollipop and starts to upgrade the apps (again let it do it’s thing first time boots take a while on android)
  12. Check your rooted by starting the supersu app.

Now you can let your bootloader unlocked or lock it, it’s up to you.
I lock it again just to be on the save side.Have fun with your lollipop.