Rollback software update 15.20

Since updating to 15.20 I'm having similar issues with battery life as also raised by numerous other people on this forum. How can I rollback my update to before this as I'm barely getting 2 days of battery now out of my device which is not as advertised and was working absolutely fine before the update. No I don't need to try any of your tips and tricks the update has caused this issue nothing else.