first you have to find the right hammer,if you don't already have one.
most of the time it is an easy job. just remove the side plate screws and rap the grip frame where the grips rest until the side plate comes loose. lift it off and lift out the hammer block. back off the mainspring screw until the mainspring can be lifted out, then with the cylinder in place pull the trigger moving the hammer back until you can lift it out,don't force anything,with the trigger held back replace the new hammer and let it down. replace the mainspring and re set the mainspring screw and replace the hammer block. when replacing the side plate do not force it the hammer block will have to line up with the slot in the side plate finger pressure only, replace the screws and try the action, you may have to stone some contact points but more than likely it will be a drop in fit.
i could have replaced the hammer in the time it took to type this. if you were close to newnan,ga. i would do it for you.