1) In My Collections, click on the Collection to enter Collection View.

2) Click the "Editing Off" toggle button at the top right:

3) This will toggle to "Editing On" mode:

4) Click "Delete Collection" button. A box will appear asking you to confirm or cancel your decision to delete the Collection - be careful because this action cannot be undone.  Important Note: if moments within the Collection being deleted are not also assigned to other Collections, they will be also be deleted along with the Collection.