I just used iTunes Producer to swap out the cover of my book, Mountain Laurel. The process is simple, easy, and quick. Within 2 hours, the new cover of my book showed up in the iTunes iBook Store. These instructions can also be used to change the metadata (description, categories, etc) of your book.
Before you begin, you'll need to find your book's Apple ID number. To do this, log into iTunesConnect.Apple.com and click 'manage my books' on the dashboard. Each book has an Apple ID. You should also have your new cover close at hand.
1. Open iTunes Producer and click the Look Up Metadata.
2. Enter your book's Apple ID number.
The book's metadata will automatically open in iTunes Producer and you can now make the necessary changes. To upload a new cover, simply go to the Assets portion and click Cover. Insert the new cover image. Then click Next until you get to the "Deliver Content" at the end. Click to validate and deliver. Done!
See? Very easy.