Ios9 software failed
iPhone 5s, iOS 8.4.1
Millions of people thinking they need the upgrade RIGHT NOW. Simple as that.
Wait. There are millions of users attempting to update at the same time. The servers are getting clogged. You will just have to learn to be patient.
You are facing an overloaded server which is pretty typical of the first day a software revision comes out. Give it a day or so to settle down and try then.
wait.
Ios9 software failed