When you have a broken window in your door, you can fix this problem yourself and save money on labour. These steps apply to most doors; you may find a door that is slightly different, but the steps still apply for replacing the glass. The most important thing to remember is to take your time.
Remove the moulding around the window. This is hardest part you will have to do. Take a flat-tip screwdriver and place it by the edge of the moulding. Gently tap the screwdriver with a hammer to get underneath the moulding. As soon as you have it up a bit, continue around the entire moulding until it is all raised a little.
Take the screwdriver back around the moulding and lift it up more. This process takes a while to complete, but you need to take your time so that you do not break the moulding. When you have the moulding raised far enough, you can then remove it.
Remove any glazing compound and glazing pins that are holding in the broken piece of glass. The pins pull out rather easily. The compound can be removed with the flat-head screwdriver.
Place the new piece of glass in the frame. Use the old glazing pins or new ones to secure the glass in place. You will place the pin by the edge of the glass and wood frame. Tap it very lightly with the hammer. Avoid hitting the glass. Some pins may push in easily, but some may need a tap.
Apply the glazing compound around the window edge where the glass meets the wood. Allow to dry for a few minutes. Replace the moulding by tapping on the nails evenly as you go around the window. Just give the nail heads one or two taps until the moulding is in place. Then finish hammering it into place.
Take your time with the moulding. If you rush, you could damage the moulding.
Always use the glazing compound so you prevent leaks.