When attempting to delete a list you may get an error: "Cannot delete list. This list is being used in these places [name(s) of list(s)]". To proceed, remove the list you want to delete as criteria on the other list, then you will be able to delete the list.
You may also get an error when attempting to delete the list if the list is the starting condition for a workflow. If this is the case, remove the list as the workflow starting condition, then you will be able to delete it.