How to detach a digipower battery from a nikon d40?

I just got a nikon d40 from a professional photographer and it has a digipower battery attached that i want to take off.

I would consider Maximal Power Replacement Battery Grip Combo for Nikon D40, D40X, D60, and D5000
With shutter
Including 2pcs ENEL9 Lithium batteries and 6pcs rechargable AA batteries
100% OEM compatible. Guaranteed to meet or exceed original specifications.
1 Years Manufacturer Warranty.

http://www.amazon.com/...0036ME078/

http://rover.ebay.com/...m270.l1313

Battery grip? That's connected to the camera through the tripod screw hole. The battery grip should have a wheel or something that you can turn to unscrew it off the camera body.