Marshmallow was automatically installed a couple of weeks ago and has no discernible improvements whatsoever and a whole host of problems (not least that the casting function is now either flakey or non existent and appears and disappears randomly) Because of the casting and dlna problems I want to do a factory reset and revert to lollipop. How can I stop the np automatically 'upgrading" to marshmallow? I know I have the option to turn off app auto updates on Google play but I can't see how to stop it installing marshmallow. Thanks very much.