Several users have reported that they are unable to update/download apps after successfully updating to iOS 6 on the iPad, iPod or iPhone.
To fix this problem:
1-Delete the apps that are frozen, stuck, or not updating.
2-Go to the App Store, find the same app(s) and re-download and install. Please see this article for more info.
Related: A New User’s Guide to the iPad: iPad 101, iPad Basics