iOS 8 runs on the 4S and above so you can.I haven't updated to iOS8 as it's not suitable for the 4S. I've actually deleted the update so I don't accidentally install it without thinking. Unfortunately neither the 5S or the 6 comes with a country blue tick so are no good to me living in a rural area with very limited reception. I might end up having to change to a Samsung Galaxy 5 when the 4S eventually dies.