All books read by HBreader are stored on EPUBCLOUD. You can not remove a book from the cloud. You can remove a book from the local bookshelf, so that you have less books on device, this saves memory space on device and also makes HBreader faster.
To remove a book from bookshelf, long click on the book, then click the bottom right button, marked as trash can. Do not worry, the book is only deleted from the device, it is not deleted from the cloud.
To restore the book back to the device, choose "Cloud books management" from the main menu, this will open a browser window with your books, each book is displayed with icons on it's left hand side. A book deleted from the device is displayed with a cloud icon. Short click the cloud icon to restore the book, switch back to the reading application and within few moments you will see the book restored and downloaded again.