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.