Camera filters missing in iPhone 4s
What version of iOS are you running? Live filters was added on iOS 7. If you haven't updated your iPhone to the latest (or, now, second-to-latest) major version of iOS, the "live" filters will not be available.
You can check your iOS version by going into Settings > General > Software Update. But, be wary of updating to iOS 8 (which is now the version available to be upgraded to) many (though not all) iPhone 4s users have had issues with iOS 8.