Shouldn't be too terribly difficult. First, let's look at the Factory Service Manual for your car:
http://www.nicoclub.com/archives/nissan ... nuals.html
Section BL, pages 175 and on, discuss the componentry. However, without knowing what part has failed, you might be replacing parts for no reason.
Do your other door locks work (either with the key fob or by pressing the button on the driver door)? Do you hear any sound at all when you press the button on the hatch?
Page 190-191 of that section describe the actual removal of the lock and switch, but again, I'd want to diagnose it first. If you hear a sound, but it doesn't unlock, that would indicate maybe a piece of debris in the latch mechanism or a sticky latch.
Let's figure this one out!