The Bing Maps Windows 8.1 Store SDK brings a lot of improvements over the Bing Maps Windows 8 SDK. The following instructions can be used to migrate your existing Bing Maps Windows Store apps to Windows 8.1.
1. Upgrade to Windows 8.1
2. Download and install Visual Studios 2013.
3. Download and install the Bing Maps Windows 8.1 SDK.
4. Create a copy of your Windows Store App and store it in a separate folder as a backup (optional).
5. Open your Windows Store App in Visual Studio 2013.
6. Right click on Solution folder and select “Retarget Windows Store App for Windows 8.1”.
7. In the window that appears, select all the projects you want to migrate to Windows 8.1.
8. Go through all projects in the solution and update the references to the Bing Maps SDK as follows:
a. For C#, C++, and Visual Basic Apps
i. In the references folder delete the references to the Bing Maps for C#, C++ or Visual Basic that have an asterisk beside them. Also remove the reference to the Microsoft Visual C++ Runtime Package.
ii. Right click on the references folder and select Add References.
iii. Go to Windows -> Extensions and select Bing Maps for C#, C++, or Visual Basic (version 1.313.825.0 or above). Not that a reference to the Microsoft Visual C++ 2013 Runtime Package for Windows will be automatically added.
9. Build your app and ensure there are no errors.
10. Run the application and test that it runs as expected.
Additional information on how to migrate apps can be found here.
You can find information on new features in Windows 8.1 here.