The conversion up should be quite smooth.
ie not much (if anything) for you to do.
The only know "common" change is the CSS for the "Footer" - and that's documented on the pre-release page.
Actually I don't think the app is "damaged" in any way, until you start making changes the app will probably work in NT4 just fine.
And you can install NT4 over NT5 - that'd be fine too.