I just got the same sights, the plunger did not fit in the windage screw provided by MEPROLIGHT. I had to go to a local gunsmith and get a new screw.
Removal of the front sight is accomplished using either a pin push to remove the factory pin or drilling out the factory pin and then put in the new front sight. Once the new pin/sight blade are installed the pin can be slightly expanded using a punch. If you don't have access to proper clamping and a drill press I'd let the work be done by a gunsmith.
I'm curious how your firearm shoots with the new sights, mine (6" .44 with 240 grain factory loads) shoots a good 3-5 inches high 25-50 yards when shot from a stand and I have no adjustment left on my elevation screw