Hiding Books

Hi,

I need help moving the books from my library so that they are hidden, as I understand it is no longer possible to delete purchases? I understand that books can be hidden by going into purchased on iBooks and hitting the little x on the book, however the books in my library have already been dowloaded to the library therefore they are not in the purchased section. I would like to know how to get them back there in order to hide them, or any other way that I can hide already downloaded books and get them out of my library

Thank you.