If you have recently upgraded your version of Visual Studio and find that Mi-Forms Designer is still opening the script project in the previous version of Visual Studio when you configure it to use Visual Studio for editing, you may have a file type association that needs to be updated.  It is likely that your ".sln" file type is still associated with the older version of Visual Studio as the default application used to open it.

The following link shows the basic steps involved in changing a file type association in Windows 8:

 http://www.wikihow.com/Associate-File-Types-in-Windows-8

After following the steps and changing the ".sln" file type to be associated with your newer version of Visual Studio, you should find that Mi-Forms will now correctly launch the new version of Visual Studio for your script editing needs.