My iPhone says its up to date but its not?

I have the iPhone 4s and every time I go into settings-general-software update, it says my software is up to date with iOS 6.1.3! All my friends have gotten iOS 7 already! Why doesn't mine say I need to update to iOS 7! And how can I make it say that?
And I know that the iPhone 4s can get it.

Strange! Try plugging it into iTunes and check for update. (Make sure iTunes is up to date)

My iPhone4 says up to date for iOS 7.1.2 but it's not