I got some XS 24/7 express night sights for my P99 AS, and they are very easy to install. In fact, the back sight is adjustable just like the factory's. You just transfer the adjusting screw to the new sight.
To remove the rear sight, push down on the the little dowel pin at the bottom of the sight screw,it has a little relief cut/slot in it where the head of the screw rests. That's what basically holds the sight in place. It is spring loaded and should not be all that stiff. You should be able to press it down with your thumb nail. Hold it down, and push the rear sight to the left. It's that easy.
Only thing with the XS sights, they are a V-notch rear sight with a bar, instead of your vanilla 3 dot set-up, so you might not like them. I prefer this type of set-up because I notice it helps me shoot a little more accurately. Plus they're made of metal instead of the cheap plastic the factory uses.
As for the front sight, a socket and some locktite. If you get the XS sights, they'll come with a tool/socket for installing the front sight.
Hope that helps.