To remove a saved book, navigate to the “Home” section. Tap “My Books” to find a collection of your saved books. Press "Change" and choose the book you would like to remove.
You can also remove a book when you have it open in your app. Either by tapping “x/ Remove” below the cover, or by long pressing the cover anywhere in the app and tapping "x/ Remove from My Books" from the book menu that pops up.