How do i delete books off my ''purchased books'' on my iphone?

I have recently purchased a book off itunes and it was stored in ibooks. Upon reading the novel, i discovered it wasn't very good and i deleted it from my, ''books'' library. Unfortunatly, when i enter my ''Purchased Books, it is still there, and i can download it to my books. I do not want to do this. Is there any way of deleting the book permenently from my ''Purchased Books?'' Thanks!