To get your copy of Dorico back to a virgin state, all you need to do is trash the Dorico 4 folder in the %APPDATA%\Steinberg folder. You might also want to trash any folders in the same location from older versions of Dorico that were installed on your computer, as Dorico might try to migrate your settings from the previous version to the new version when you next run it after having trashed that folder.
Just keep those folders somewhere out of the way in case you want to recover any saved settings.