ASP.net website upgrade from Asp.net 3.5 to 4.0

We currently have a demo website running on ASP.net 3.5. We would like to add Mobile capablities to the site. Spacificly we would like a Mobile navigation and mobile master page that can work along side our other features for normal browsing. Our current nagigation has a parent child relationship we have 6 root elements. We would like to add an optional 7th element for Mobile Browsing. If the Mobile Browsing root element does not have children the mobile navigation will be a combination of the children of all the other root elements. This project can only be a success if all the existing functionality remains along side the new Mobil features. All code must be writen in ASP.net /VB. We will require that you track changes to all files modified. Files in the App_code directory cannot be modified, however, you can add new files if needed.