via iTunes

• Connect your device to your computer and open iTunes on your Mac or PC.
• Click your device in top bar of iTunes.
• In the left sidebar, click File Sharing.
• Drag and drop sound file file or folder with sound files onto the Documents list to copy them to your device.

via WiFi

• Go to "BOOKS"
• Swipe book to be deleted from right to left
• Tap to "Delete" button and confirm operation