You can delete a book in your bookshelf by
(1) At grib view, doing a long press against a book cover and then selecting "Delete" from the pop-up menu;
(2) At list View, swiping the list from right to left and then selecting “Delete”.
(3) You can also delete multiple books at once. To do so, just tap on the “...” (more icon) at navigation bar of bookshelf, select the “Select” icon, and then tap on “Delete” at tool bar, which is located at the bottom.