I "bought" a free book on iBooks Store, the book is on my iCloud.
Now I would to remove it, but I cannot find a way to do it.
First, delete the local copy by selecting it and pressing
Now if the book is displaying with the iCloud icon you can hide the iCloud purchases, by clicking on the "Sort By" menu and making sure "Show Purchases in iCloud" is unchecked. If that was already unchecked, then the book's icon will simply disappear.
On the Mac you can tick
You can hide all unwanted books in iTunes on the Mac forever…