Easiest way? Sight pusher. (Especially if night sights are being installed, so the gas tubes aren't damaged by shock improperly delivered during installation.)
Hardest way? Lined bench vise, brass drift & a 4 oz ball peen hammer. (Makes it relatively easy and quick to damage a slide if you're not experienced at doing it this way, though, if only from a cosmetic perspective, but also an easy way to slip and roll an edge of either dovetail when whacking the drift punch.
S&W sight bases usually require some effort to get them moving, especially in older guns.)
Even the use of a sight pusher can be difficult for some folks, though, and/or with some guns. Also, depending on the design of the sight pusher, some "loading" of the screw and then the judicious application of a bit of impact force may be needed to get some rear sight bases moving.
The S&W sights come out of the dovetails to the right (left-to-right movement) and are installed from the right (right-to-left movement). The dovetails are narrower on the left end. This is looking at the pistol as if from the rear, with the muzzle pointing away from you.
There are 2 springs (different size) located underneath the rear sight. The 3rd gen .45 slides usually have an oval plate which covers them, making it easier to hold them in the properly compressed position during sight installation. Bending or clipping one of the springs can become a problem for proper plunger movement and tension.
Some potential problems might be most easily avoided if sight removal & installation is left to a skilled gunsmith familiar with the particular pistol design.