Remove them, you can remove non-persistent volumes if you want... otherwise, click on Volumes, and remove the "unused" volumes in question after the containers are removed.... When that's done, click on "Images" and remove the "unused" images in question.
Finally, delete any directory that you associated w/ those containers.
They're gone. That's one of the beauties of containers.
I've done everything except deleting directories. Sorry to ask, but where would those be located?