Hi all,
as you know App Studio v4 (released some weeks ago) is optimzed for iOS 7. If you already have publsihed an app with App Studio all you need to do is recompile your app using the App Manager on my.appstudio.net.
Please note that you probably also should update your artwork to give it an iOS7 look&feel.
Now Apple announced that if you submit a new app (or new update to your app) on Feb 1, 2014 or afterwards, it needs to be iOS7 optimized:
https://developer.apple.com/news/index.php?id=12172013a
Regards
Matthias