Just from the library. Simply pick them and then go to Edit on the top menu and choose Delete. Because they are not items that you have purchased, they will be removed from your iTunes library. Whether you bought it from the iBook Store – Sorry – but Apple’s policy has always been that purchased goods cannot be deleted from iCloud.
Deleting Books in iBooks
How to delete books in iBooks
Open iBooks and go to File > Delete a Book. When you right-click, you have a variety of choices and the option to delete is at the bottom. It then asks if you wish to permanently remove it from iCloud, and it is removed as well.
Remove a book or audiobook from your iDevice by going to the iBooks app, tapping Select, and then scrolling down. Locate the item you wish to remove and tap it. Choose Delete, then choose one of the options: Remove Download It Only From My Device Tap Remove Download To delete it only from your device.
Select the check box for Delete from My Account, then click Yes when prompted. In the column to the right of your name, select Delete and then Delete (from My Books) in order to delete your library items. Select Update Settings from the drop-down menu at the top left of the window. Click Library at the top of the window; then All Books in the sidebar. To remove a file, select it and click Remove or Remove (from My Documents). Open up Edit > Delete on your computer’s menu bar; confirm when prompted.
To remove a book, go to iBooks and select the edit option then choose the book and hit delete. I erase books from my Purchased Books list in the same way.
To remove a collection and return the books within it to the Books library, open the Collections dialog by tapping Edit. To get rid of a collection, tap the minus sign next to it until no longer shown, then press Delete.
When you remove a book, audiobook, or PDF from your library, it is no longer saved on your Mac. In the Books app’s sidebar, choose All Books. Select the item you want to delete and then press the Delete key.