Deleting audiobooks from iPod

I have an iPod (I think Classic). I download books from my local Library using Overdrive Media. There are 4 books on my iPod that I can't get rid of, even though they have expired. They don't show up when I click on see the content when it's hooked up to the computer and they don't show up in Overdrive. I can't see the new downloads on my iPod because these other books are still showing up.