As long as your book has no sales, you can delete your book. To delete your book, go to where you work on your book in Leanpub and click on "Admin" in the book tools menu on the left. Then, click on the "Delete Book" submenu, and click the big red button you will find there. If your book has sales, we have to offer it to its existing readers in their Leanpub libraries, so you can't delete it. You can also unpublish your book if you don't want to delete it; see below.