To replace broken glass on windows safely, remove the whole window frame, and place it on a flat surface. Use work gloves to pull out one piece of broken glass at a time. Remove all the putty from the window frame with a wood chisel or a putty knife. To protect the wood frame, remove the putty in small pieces. Remove the old glazier's points that keep the glass in place, and smooth out the surface with the chisel.
Use a heat gun or soldering tool to soften putty that is difficult to remove. Apply a layer of linseed oil to the window frame with a brush, and let the wood absorb it to prevent new putty from drying out quickly.
Apply a thin layer of putty around the area were the new glass goes to cushion the glass pane and prevent air leakage.
Make sure the new windowpane has the right size to fit the frame. Insert and firmly press the windowpane. Insert glazier's points on each side of the glass, then insert a glazier's point every 4 inches. Press the glazier's points into the wood with a glazier tool.
Prepare thin strips of putt, and apply it around the new glass, starting from a corner. Dip the glazier tool in linseed oil, and use it to spread the putty from corner to corner, making sure the putty isn't visible from the other side. Remove excess putty from the corners and edges. Use sandpaper to smooth out the surfaces.