Q: how to eliminate completely an ebook from iTunes

Mauro,  

Thank you for visiting Apple Support Communities.  

I understand that you want to delete an ebook from iBooks on your iPad and Mac.  Here are the steps on how to delete iBooks from the iBooks application on your Mac.  This information can be located via the iBooks Help menu via the menu bar of iBooks.  

• To delete a book, select it, then press Delete.

The article below will walk you through the managing your iBooks library on your iPad.  

Delete books and audiobooks

Remove books or audiobooks from the iBooks app using the steps below:

1. Tap Select.
2. Tap the books you want to delete. 
3. Tap Delete.
4. Tap Done.

Delete music, movies, apps, and other content from your iPhone, iPad, or iPod touch

You can also hide any purchase via the steps below.  

Hide and unhide purchases in iTunes or iBooks on your Mac or PC

Cheers