Ridding old iOS Manuals from Books

I downloaded the user's manuals for iOS7 and iOS8 into Books and recently updated to iOS9 and downloaded its manual. I would like to get rid of iOS7 and iOS8 from showing up on my iPhone, especially, since I cannot tell the manuals apart from their icons and have to just keep trying until I get the right one. I cannot seem to delete them from Books, which just seems to keep them in the cloud (and on my iPhone). There must be a way to get rid of manuals describing outdated operating systems, but I don't know how.