You can remove the audiobooks from the iPad, follow the simple steps below

• Connect the iPad to the computer you normally sync with iTunes.
• With iTunes open, click on your iPad from the menu.
• Select Books from menu.
• Scroll down to Sync Audio Books and make sure its checked. Click on Selected Audiobooks.
• Manually uncheck audiobooks you do not want synced up to the iPad. This will delete the audiobook from your iPad. The audiobook will still remain in your library on your computer.
• Click Apply, this will remove audiobooks from the iPad.