you can use a sharp wood chisel to remove old putty. if you try to use a heatgun, you will also loosen the paint, that is ok if you are going to clean and repaint. be careful not to remove the glazing points (little triangle or similar metal tabs) that secure the glass to the wood. NO caulk, use either new putty or the newer glazing compound. to get the smooth edges on the putty or glazing compound, use the flat blade of a 1 inch putty knife. if you dampen the blade of the putty knife, it is as easy as putting icing on a cake :o).
Carl