The other night I wanted to install iOS 11 on my 6s+ overnight, but I had to accept the Terms of Service to do the installation. I woke up at 5, had to be up by 5:45, and didn't want to miss out on 45 minutes of sleep. I did not want to start the installation for fear of my alarm not going off due to the update. When I was fumbling around with my phone I accidentally clicked the install option, which took me to the Accept Terms of Service screen. I tried to exit out of that screen, but couldn't. So I hit Decline. Now when I go to Settings -> General -> Software Update, it says my software is up to date (10.3.2).
How can I fix this situation and upgrade my iOS now?