This has been happening to me. I know that if I allow the update I will lost my Office 365 and Norton antivirus, ok, If I don't lost them I have to re-install them. I do not want to do it. So when it took control of my computer and began the upgrade without my authorization, I took off the battery and disconnected my laptop. Then I turned on my laptop again and again took control of my laptop and began the upgrade, Again I disconnected my laptop. I did this 3-4 times. Then I worked offline for a while. This happened to me yesterday, today I turned on my laptop and it hasn't bothered me.
I don't want the upgrade!! How can I avoid it? Thanks