Place masking tape across the window on the outside of each French door panel. The tape should extend 6-inches past each side of the window and onto the door. This helps keep the door glass in place when removing the grids.
Check the inside face of the door glass frame for small round seams. The seams are plugs that cover retaining screws. Pry the plugs off the door glass frame with the corner of a utility knife blade.
Remove the frame's retaining screws with a Phillips screwdriver, while your helper holds the outside frame in place. Pull the top of the inner door glass frame toward you with one hand while holding the glass against the outer frame.
Pull the grid out of the inner door's glass frame. Insert the new grid into the inside of the inner door's glass frame. The ends fit into the recessed area on the back of the frame. Push the inner frame back into place and secure with the retaining screws.
Place the caps over the screw heads.