Remove the stationary door first. (Most sliding doors can only be removed from the outside, which will require you to remove the stationary door first.) Unscrew the screws that hold in the stationary door. Use a screwdriver to push up from the bottom of the stationary door as you have another person hold it from the outside and pull out.
Move the wheels up into the sliding door. They can easily be pushed upward into the bottom frame of the sliding glass door. This will give you enough room to lift the door and pull outward.
Remove the screws on the sliding door. There are two pairs of screws on each side of the bottom of the sliding door. Unscrew the screws, which will also allow you to remove the bottom part of the frame to the glass door.
Place the new rollers inside the bottom of the frame. Screw both the bottom part of the frame and the rollers back into place. Replace the sliding door by lifting the rollers into the bottom of the frame, putting the bottom of the sliding door into the track, and fitting the top into the track as well. Replace the stationary door by putting in the bottom first and re-screwing the screws to keep it stabilized.