In most cases, opening a VS2010 project in VS2013 is not a pain.
You can find 2 kind of apps in the Windows Store :
- Modern UI apps (aka Metro)
- Desktops Apps
If you want to create a Modern UI app you need to target the .Net 4.5 framework. To do so you need to upgrade to VS2013.
But most of your work will be to rewrite a huge part of your program as the modern UI is not compabible with WPF (and you will need to manage touch devices). Other assemblies also doesn't have all the features of the desktop ones, so you will probably have a little bit of work in that area too.
Here is a link that explain the process of publishing an app in the Windows Store : http://msdn.microsoft.com/en-us/library/windows/apps/jj657972.aspx
If you want to publish a desktop application it seems to me that you only need to provide an URL to download your package. Be careful it is not possible to submit that kind of app with a personal account, you need a company account to do so. You can find more information about that process on MSDN: http://msdn.microsoft.com/en-US/windows/desktop/dd535817