Measure the existing doors so you can purchase replacements of the same size.
Loosen and remove the screws attaching the metal doors to the hinges of the cabinet. Take the metal doors off the cabinets.
Hold the wooden doors against the hinges. Place a level on the outer vertical edge of the door to ensure it's plumb. Mark the location of the hinge holes onto the door with a pencil.
Drill shallow holes in the back sides of the wooden doors with a 1/8-inch drill.
Place the doors on the hinges, lining up the holes in the doors with the hinge holes. Insert screws in the holes and tighten the screws to hold the doors in place.