I'm afraid that you can't delete anything from your purchase history. The most you can do is hide items so that they're not visible. Here are the instructions to hide and unhide your purchases. http://support.apple.com/en-ca/HT201322It's been awhile since I used iBooks and boy has it changed a lot. I appear to have books in my purchased section that I want to delete but I cannot see how to do that.
Any help greatly appreciated.