Upgrade a project (Windows Phone)
You will need to use Visual Studio 2012 or Visual Studio Express 2012 for Windows 8 to upgrade your Windows Phone 7.1 project to a Windows Phone 8 project.
After you upgrade a project, you cannot later downgrade it back to Windows Phone 7.1. Because of this, you should create a back-up copy of the project before you upgrade it. When you upgrade a game project, the entire solution will be upgraded.
Upgraded projects may need additional adjustments if Windows Phone 8 features are added to the application. An upgraded project does not add in any of the Windows Phone 8 references. It may be necessary to add references to your project for new APIs that you want to use.
An upgraded project does not add capabilities to the application manifest file. If new Windows Phone 8 features are added to the application, it may be necessary to manually edit the manifest file or run the Capability Detection Tool.
For more information about updating your Windows Phone projects, see How to upgrade an app project to Windows Phone 8 on the Windows Phone Dev Center.
To upgrade an existing Windows Phone 7.1 application
Open the Windows Phone project that you want to upgrade in Visual Studio.
In Solution Explorer, right-click the project and then select Upgrade to Windows Phone 8.0.