You can't delete a course without deleting its contents.
You can delete bulk cards in a section.
1. Go to "card list" page from "Course Management" on the left column.
2. Push "Select All", or check the boxes of the cards that you want to delete.
3. When a box is checked, you can select "Delete all selected card".
4. Make sure if there's any problem on "Card Bulk Delete" page, then push "Delete" button.