I did mine (M&P 40) with a brass drift, hammer, and a vise.
BOTH sights need to be removed from L-R (when viewed from rear.)
remember to loosen the set screw on the rear first.
I used a pencil line to mark the center of the original site position
The amount of force seems to vary greatly from gun to gun.

I have found that the rear sight will become very easy to move before the Upper striker block spring and cap are visable.
use any flat tool (or your finger) to capture these when rear sight is removed. I recomend you do this in a very open area so that the parts can be recovered if they fly away.

New sights go on from R-L
put spring and cap in place and slide rear sight on as far as you can by hand (far enough to cover cap at least.)

On one gun I had to use two vises, one to hold the slide, and the other to act as a pusher. That was the only gun I had to do that with.

__________________
Gerry