You must be an Admin to delete a Guru Collection.
How to Delete a Collection
Navigate to the Team Settings page.
Select the Users & Collections tab in the left sidebar. Select Collections in the top tab
Click the gear icon on the Collection you would like to edit or delete.
In this view you can make changes to the Collection's title, description, or assigned color. Click Delete Collection to delete the Collection.
Deleting the Collection will permanently delete all the content contained within the Collection, including archived Cards. Once the action is confirmed, the Collection cannot be retrieved.