I have a few apps written in iOS6. I am discovered that all the iOS6 apps do not look right in iOS7, things are out of place or the UX/UI is all wrong.

I am unsure of how to make these apps compatible with both, rather I'd much like to keep iOS6 apps as iOS6 and just don't let them run in iOS7; but I'm not sure how to do this.

But my real question is how do you make apps that will work in iOS6 and iOS7? Do you use like If statements, different NIB files?