After the new IOS downloaded in iPhone 4S it won't connect to Wi-Fi?

My sister has an iPhone 4S and she downloaded the new IOS and now it won't hook up to Wi-Fi. Any idea why? Is there a way to fix it?

Hold down he Home Button and the Power Button for 10 seconds or until the Apple Logo pops up. This will basically just Reset/ReBoot the device.

It's an IPHONE, not an IPOD. It doesn't use that to work.