Remove the old door by gently tapping on the hinge pin with a small screwdriver and a hammer. This will remove the pin and separate the two halves of the hinge so that the door can be removed.
Measure the location of the hinges on the old door with a tape measure. Transfer these measurements to the new door so you will know where to reinstall the hinges.
Remove the hinge parts from the old door. Use a screwdriver to remove the screws that attach the hinge to the edge of the door.
Drill small pilot holes in the new door at the screw locations for the hinges. Use the screws to attach the hinge plates to the new door.
Hang the new door in the opening by aligning and joining the hinge plates on the door with those that are on the door frame. Reinsert the hinge pins, tap lightly with the hammer to set the pins, and the new door is installed.