Imo 5.1 AOSP as said above. Load the PG05img file on the root of your SD card and press volume down and power on. hboot will see the file and ask if you want to load it volume up for yes. After it loads remove the file from the root of the card or rename it and you should be good. Nat3mil has a good video on YouTube for this. You might want to check it out in case I forgot something. Good Luck!