Can’t delete purchased books from my Books library.

I have downloaded several books from Apple Books to my IPad Air 4 into the Apple Books app and can’t delete them or hide them. They were free first books that are associated with a series and I actually didn’t pay anything. When I upload other books from other sources I can add and delete just fine but these “purchased” books are driving me crazy. I don’t want to read any more of the series and I want them out of my library. When I go to “Hidden” books I can see the ones I’ve hidden in the past but none of these in my library gives me the option to delete or to hide.

Please, can anyone help with this or am I doomed to have them stuck in my library forever?

Ron H.