You could have fooled me. Just two hours ago, my girlfriend's laptop has a pop-up window that said Windows 10 would be installed in 10 minutes with a countdown timer. The one button on the window was "restart and upgrade now". And I wasn't going to click the x to close it in the upper right because we all know that now also starts the upgrade thanks to the recent articles on it. So normal users are screwed. If it happens to you, there's a small hamburger menu icon on the upper left. Click it and go to settings (iirc) and select the small text that says "cancel upgrade".
Microsoft has gotten so monumentally shady about these upgrades that I'm reconsidering using or recommending windows 10 at all to anyone.