Delete a list in the List Options menu. Select "Delete" from the drop-down menu.
There's no need to delete lists, unless you're certain you no longer need it. Perhaps you find it confusing to have too many lists, and you've already duplicated the ones you need. Just be sure that you won't need it again, before deleting it.
After you delete a list, you might still be able to restore it.
From the "Lists" pane, click "My lists on top".
Find "Recently Deleted" in the drop-down menu to see deleted lists. Beside the name of the list you wish to restore, click on "..." and select "Restore".