Pull the drawer out of the desk as far as it naturally goes.
Feel the back of the drawer, looking for a cable attached to it. If you feel one there, unscrew it from its drawer attachment with a screwdriver. If you don't feel anything in the back, continue to the next step.
Reach your hands into the desk, and search for latches on both sides along the track the drawer slides on. Some desks require these latches to be pressed in to get the drawer loose.
Lift the drawer upwards off the track, and then pull it out of the desk. Drawers without latches often lift right out, and ones with latches should lift out once the latches are released.