How to delete Assignments and Courses if there is any submission

Hi, I've just started using Web-CAT last week.

I created a Sandbox course and was told that I can delete the course if there isn't any assignment.

In order to delete an assignment, it can't have any submission. So how can I delete any course or assignment if assignments exist? (I also cannot find any "delete" button)

I'd tried to delete once from the database but ruined everything.