Remove the Trim
Cut the paint from around the outside of the trim and from the joints where the trim connects, using a utility knife. Loosen the trim from the door with a putty knife. Tap lightly with a hammer if required. Pry up any trim that has nails high enough to fit a hacksaw blade into the gap. Cut the nails and remove the trim. Pull the nails through the backside of the trim using a pair of nippers. This avoids damage to the front of the trim. Label each piece of trim when it is removed. Writing T (top), B (bottom), R (right) and L (left) ensures each piece gets put back in the right position.
Cut the Glass
Use protective eyewear and gloves when cutting glass. Measure the inside of the setting with a ruler. Make the measurement ¼" smaller on all sides than the actual inside measurement. This gives the pane room to move. Set the large pane of glass on a piece of particleboard. Use the ruler and a grease pencil to mark the measurements on the glass. Measure from the long edge of the glass, measuring the width at the top, middle and bottom of the piece of glass to be cut. Use the grease pencil to put a small mark in each location. Use a straight edge and line it up against the three marks on the glass. Put a drop of oil on the glasscutter blade and score along the straight edge. Do not exert too much pressure or the glass will crack. Slide the glass to the edge of the particleboard and lightly tap it to snap the glass. Repeat the process for the second cut.
Replace the Glass
Completely remove any caulk or debris from the setting. Put a small bead of latex caulk around the frame to help hold the glass in place. Place the glass back in the setting. Replace the trim around the frame using the labels as a guide. The handyman can use Liquid Nails or a similar product to adhere the trim in place. This avoids splitting the trim with nails or accidentally hitting the glass. If nailing the trim, first blunt the ends of the nails to avoid splitting the trim. Do this by hammering the tip against a hard surface like brick or concrete. Tap the nails into the trim. Set the nail heads using a nail punch. Run a thin bead of latex caulk along the outer trim seam. Fill the nail head holes with wood filler and paint to match the existing trim.