Lift the sliding doors out of the tracks and put them aside. Unscrew the door tracks that need replacement. They should be simple enough to remove once you have removed the screws holding them in place. Get a similar door track from your local; home improvement store. Measure the necessary length of the new track and cut it to the right length using a hacksaw. Lay the new track in place and screw it down into the surface. Make sure the track is firmly fixed in place.