Today is the day for Nexus devices to get their taste of Android 5.0 Lollipop. The Nexus 7 2012 is one of those devices and the factory images and OTA updates are making their rounds. The OTA update will most likely take some time before they're pushed out by Google, but you can bypass the waiting game by loading on the factory images for your specified device, which in this case is the 2012 Nexus 7. Things worth noting here, if you load up a factory image, you'll be getting official Android 5.0 Lollipop. The factory images are straight from Google so essentially it's just like the OTA, without the over the air part. Secondly the factory images are going to basically reset your device, which means all the data within it will be wiped. You know what that means. Yes, you'll want to make sure to do a backup before you attempt to go through with the process.
If you're OK with wiping your device and starting from scratch, you can head to this link to grab the factory image for your device. Everything is listed by device type, and numbered off so the correct image will be easy to locate. Make sure you grab the correct factory image(i.e. wifi or LTE model of the 2012 Nexus 7)to load on. After you have the image downloaded, follow these steps:
1. Unzip the contents of the factory image file you downloaded and make sure to Unzip them into your SDK/platform-tools folder
2. Open the command prompt from inside the platform-tools folder
3. proceed to type up each one of these commands. Type the command, wait for it to complete, then move on to the next command.
*If using a Mac, be sure to add ./ in front of all commands (ex: ./fastboot reboot-bootloader)
adb reboot bootloader
fastboot flash bootloader bootloader-<insert-image-name-here>.img
fastboot flash radio radio-<insert-image-name-here>.img
fastboot -w update image-<insert-image-name-here>.zip
4. This is an option for getting back to a completely stock build without root and a locked bootloader:
fastboot oem lock
5. For keeping an unlocked bootloader during this process all you have to do is tap the power button from the start screen.
6. That's it. You should now be back to a completely stock device.
We realize the process for loading on the factory images can seem a little confusing. If that's the case, waiting for the OTA update to come to your device on its own is the best solution, as we aren't responsible for anything that happens to your device should you try the factory image method to obtain the Lollipop update. If you already have a rooted device, you can load the OTA ROM once it becomes available, which we'll post in here for you.