Q: How to delete books in iBooks?

After you press edit, select the books you want to delete by clicking on them, then press the delete button.

Are you in the purchased books category ? If so are you trying to delete a book with a cloud sign on the top right corner ?

If this is your case, these books aren't physically on the device but it's a view of your purchased book. To turn it off you can select show all purchases to OFF from the settings app, iBook tab.

If this is not your case try to reinstall your app

This worked for me on my iMac (Similarly to iPhone as well)

Open iBooks - click on iBooks Store (top left hand corner) - click on 'Purchase' under Quick Links - Click on 'x' buttom over the books that you want to delete.

This deleted all the books i needed to disappear from my iMac and iPhone!!

Hope this works for you.

Thank you, ayano! This hint saved my day!

Thank you

But where is Quick Links?

It's on the right-hand side of the iTunes store homepage on your computer's iTunes, and if using a Mac with OS X Mavericks on it then also on the right-hand side of the iBookstore in the iBooks app on it

On itunes, login to your account. Then once you connect your phone to your computer with the cord, go to your itunes store on the comp. select the books category on top then click on purchased on the right side panel. there you will have all your books listed and you can delete the ones you don't want by hovering over them and clicking on the X that appears. once you have completed this, you must log out of your apple ID on your phone and log back in for the books to be completely cleared from your purchase history.

That does not 'completely clear' them from your purchase history (you can't permanently delete any item from your purchase history), it only hides them the Purchased links for redownloading - they can be unhidden : iTunes Store: Hiding and unhiding purchases

Actually it appears you can permanently delete books, etc. from your apple account by going to mybooks and right clicking on the book. It gives you the delete option (like when you want to remove an app) and deletes the book. At least some books I've done that with are not showing up anywhere in  my account. Otherwise my library gets clogged up with all the free books I try out.

How to you right click on an ipad?

You can't, and you can't permanently delete them from your account's purchase history, you can only hide books from the cloud via your computer's iTunes (or iBooks app if using an up-to-date Mac) : Hide and unhide purchases in the iTunes Store - Apple Support

thanks this worked for me