First thing to do is to retarget your Windows Store app to Windows 8.1. You can do this using Visual Studio 2013 Express for Windows Update 2. You can read all about this here app migration here:

http://msdn.microsoft.com/en-us/library/windows/apps/dn263113.aspx

What you will be reading in this post is about my experience.

SMS message send, receive, and SIM Management sample(Windows 8).zip(687.7KB) file from here was downloaded (this was a random selection from the bundle):

http://code.msdn.microsoft.com/windowsapps/Windows-8-app-samples-4d76cbbf

When you try to open this in VS 2103 Express for Windows Update 2 (with elevated permissions) you will asked about your Developer license and in my case this:



When you agree to this you will see an authentication form for Microsoft. Enter your credentials and click SignIn. You will be presented with this:



Changes have to be made from Windows 8 to Windows 8.1 and you will get this message.



You click OK and then you right cclick the project in Solution Explorer as shown.



Click Retarget to Windows 8.1. You will get a Security warning advising about opening only items from trusted locations.

Click OK

You will get another messaage that once targeted to 8.1 you cannot go back to 8. Make sure you read and understand this message.


Click OK.

The project gets converted to 8.1 version. This project was randomly picked from the sample bundle and it looks like no further changes are required as I was able to build and run successfully. Although this example did not require any other changes, you should be aware of API changes going from one version to another. Go back to the first link on this post and read up.