Delete books from your Mac
When you delete a book or PDF from your library, it’s no longer stored on your Mac.
In your library, select the book you want to delete, then press the Delete key.
If you’re using iCloud for iBooks and you delete a PDF or book that you imported, it’s deleted from iCloud and all of your devices where you use iCloud for iBooks.
Books you purchased from the iBooks Store are still in iCloud, even if you remove them from your Mac. They appear in your library with an iCloud status icon 
. You can download purchased books again.
You can’t delete books you purchased from the iBooks Store from iCloud, but you can hide them; just click Sort By at the top right of your library, then select Hide iCloud Books. To hide books so they’re never in your library on any device, see Hide purchased books.