Remove the sliding panel door. The sliding panel is attached to the frame with brackets. Use a Phillips screwdriver, turn the screws on the brackets counter-clockwise to loosen them. Remove the door and place it aside somewhere safe.
Remove the head panel section of the door frame. Locate the screws by removing the access strip. The screws are on either side of the frame. Loosen these and place them aside. Remove the head panel.
Remove the fixed panel door. The fixed panel door is screwed into the door frame. There may be existing caulk over the screw heads. Remove the caulk with a utility knife. Use the screwdriver to remove all of these screws. Carefully lift the fixed panel out of the frame and discard it.
Put in the replacement fixed panel and caulk around its edges with silicone caulk. Screw the fixed panel into place. Caulk around the edges to seal the door frame.
Reassemble the door frame. Replace the head panel and screw it in. Re-hang the fixed panel portion of the door.