how do I delete free books from purchases page

Hi
I would like to delete free books that I have downloaded from the purchase page. I have already deleted them from my library but they still appear on purchases. Any advice welcome. Thanks:)

Which app? They all do things a bit differently.

iBooks
Kindle
Nook
Other?

I would also like to know how to delete my purchases on the iBooks purchases page. They are off my bookshelf, but still appear on my purchases page. Any help appreciated.

Thanks.