I turned off my iPhone 6+, when I turned it back on, it said "slide to upgrade" rather than "slide to unlock". Didn't realize it, and it started to upgrade. I want to be able to control upgrading. How?
The firmware will be downloaded automatically and there is a sign on your setting app once a new update is available. However, you can refuse to install the update. iPhone won't upgrade automatically,which is illegal in US
iOS updates should download automatically but not install without you permission. What version did you upgrade to and from? In this case it could have been part of a problem with iOS 9 there were many people reporting being stuck at the slide to upgrade screen.