The phone is a Sony Xperia T2 Ultra. It's unlocked. Ever since updating to Lollipop my phone is AWFUL. It randomly stops working, when playing video it doesn't stop if I try to stop it. It takes forever to turn off and back on. The camera operation is awful too. I need to go back to kitkat. How can I do this? I also have an Oppo with beta software so I have SOME experience installing other OSs, but no clue how to do it on my Sony.