You can replace them with a screwdriver. That's for removing the grip screw. Once removed, cock the hammer and capture the hammer plunger spring. Pull to oval headed pin out of the side of the frame and remove the hammer. Do all this in reverse to install the new hammer.
Some hammers were cut down by the owner and both sear notches remain, making them dangerous since they can't be lowered safely. This one doesn't show the notches.