These models will run iOS 7: iPhone 4, iPhone 4S, iPhone 5, iPhone 5c, iPhone 5s. you can update your iPhone, iPad, or iPod touch right now if you want.
Here is a briefly step:
1. Prepare to install. If you plan to install wirelessly, confirm that you have an available Wi-Fi connection; if you intend to install via iTunes, you need your computer and the latest version of iTunes. (If you dont have it, you can download it from Apples website.
http://www.apple.com/itunes/ )
2. Back up via your computer or device.
3. Install. Settings and navigate to General > Software Update. There, you see some brief information about the update and a button to install it.
If your phone storage is full. This client side freeware could help you release some space.
http://www.macblurayplayer.com/iphone-cleaner-mac.htm