Once logged into your Moodle course 

1. Turn edit mode on in the upper right hand corner.
2. Select Bulk actions towards the top of the page.

Begin by selecting the items you want to make changes to.

3. Select and item
4. Option to select All items (except the topic headers)
5.  Choose to make Available, Duplicate, Move, or Delete

Confirmation of Deletion

6.  Click the Delete 

Bulk Deleting topics

7.  Placing a check in any of the topic headers. 
8. Click on Select all 
9. Click on Delete 

Confirmation of Deletion 

10.  Click on Delete

Your course now has been completely emptied other than the enrollments, if you accidently deleted something and want to restore it, Click on More, then the Recycle bin