How can I 'un update' my ipad I have an iPad Air 2 8.1.3 and I would like to make it 8.1.2 again. 

Is this possible?
Downgrading to iOS 8.1.2

Since iOS 8.1.3 is the latest version of iOS, you can’t simply open up iTunes and “update” to an older version. You have to add on a couple more steps, but luckily it’s fairly easy.

Before you do anything, make sure to back up your iOS device because this method will wipe your iPhone or iPad clean. Luckily, we have a handy guide on how to do just that.

First off, visit this website and download the iOS 8.1.2 IPSW for your specific iOS device. These files range between 1.5 GB and 2GB for iPhones and iPads, so be aware that it may take a bit of time to download it.

Once you have the file downloaded, plug your iOS device into your computer and open up iTunes. Go to your device’s summary page and hold down the Option/Alt key on your keyboard or Shift if you’re on Windows. Keep holding down the key as you click on Restore in iTunes.

Next, browse to find the IPSW file that you downloaded and open it. iTunes will begin restoring your iPhone and will install iOS 8.1.2.

After the process is complete, your iOS device should now be running iOS 8.1.2. From there, you’ll want to restore your backup by going to the device summary page in iTunes and clicking on Restore Backup. Give it time to restore all of your apps and settings, and eventually you’ll be back to running iOS 8.1.2 just like you were before updating to iOS 8.1.3.

Word for word from: http://www.gottabemobile.com/2015/01/27/how-to-install-ios-8-1-3-update/