I can't help you at the moment because I have to get ready for work but for starters you will need to unlock your device, acquire the proper ruu (4.1.2), or if its available on here then a nandroid backup (4.1.2) specific to your device. Then at this point the procedures to take would be based on whether you are S-On or S-off.

Hopefully someone else may chime in on this while I am at work.

Sent from my C525c using XDA Premium 4 mobile app