First, in the web app, go to the list you’d like to delete.
Next, click on the ‘Actions’ button. A drop-down menu should appear, where ‘Delete list...’ should appear. Select this option.
A popup should appear asking you to confirm your choice. After you have confirmed the deletion, the list should be deleted.
Note: you can only delete a list you created. If you're on a shared list, you can only 'leave' the list.