Deleting a tour completely from your TourBuilder account requires that the tour is unpublished from Google and completely emptied of all scenes and islands/levels.
The best way to think of it is to work backward to delete a Google tour from your account:
1. Be sure to unpublish the tour
2. Delete each of your scenes in the "Upload Photos" step
3. Once you’ve cleared out all of your islands, proceed with deleting each island
4. Click the trash can icon associated with your tour in your tour list to delete it completely