5. In the find dialog search for "midi shape shifter" and click find next
6. This should highlight a folder in the left pane. Verify that both the ProductName in the right pane and the path in the status bar at the bottom match the following screenshot. Then right click the highlighted folder and select delete.
7. Now you should be able to install the other version of MSS. Note that you may want to back up your presets/programs if you have created any custom ones.
If your up for trying that let me know how it goes.