This afternoon (1/21/14) I ran the upgrade. what a mistake. my battery level decreases fast, even without using the phone. I selected airplane mode and when I went into settings it did not actually go into airplane mode. I used to have good wifi connection and now it says unstable. Couple times my camera flash turned itself on briefly -- plus more. How can I undo the upgrade? One internet site said even with resetting the phone not all of the old features return