Below are the instructions to replace a sliding mirror door. If it sounds too complicated and time consuming, here's a link to Home Advisor, a free referral service that matches homeowners with prescreened local door contractors.
Step 1 : Unpack the doors and hardware
Carefully remove the mirror door panels from the package and identify the package of installation hardware. Read the directions for installing the top and bottom tracks and how to install the door panels in the tracks.
Step 2 : Clean and de-clutter the entrance to the closet
Remove items in the closet on the floor and clean the floor or carpeting where the new track will be installed.
Step 3 : Install the tracks
Position the track in the overhead jamb as directed. Mark and drill pilot holes for the mounting screws and install the track. Be sure the screw heads are flush, otherwise they'll interfere with the doors.
Then install the track on the floor making sure that it is aligned straight and directly under the overhead track. If the opening is not perfectly square the door may fit nicely on one side, but not the other.
Step 4 : Hang and adjust
Tilt and turn the top of the door away from you to insert the doors between the top and bottom tracks. Do the rear door first. Then align the doors with the jambs by adjusting the height of the door hanger as directed. Some track hardware has clips and bumper pads to make the adjustment easy.
Others have a leveling screw or floor guide that may need to be raised by mounting it on a wood block. Cut the block equal to the length and width of the guide, and as thick as needed. Don't forget to drill clearance holes through the block so you won't split it with the screws.
Slide the mirror doors back and forth several times in the tracks and make adjustments as needed until they roll easily.
Illustrations courtesy of Stanley Mirror Doors