Changing forks is not difficult, but getting the right one is not trivial either.
Firstly, the fork is held in place by the headset (steering bearings). These come in 2 varieties, ones which screw down onto the threaded steered tube (of the fork), and ones which clamp onto the unthreaded steerer tube. They used different tools and methods to dismantle, so know which type you have.
The steerer tubes come in different diameters, 1", 1 1/8" and 1 1/4", and can be cut to different lengths:
For threaded steerers, this is to permit sufficient "stack height" for your screw on headset.
For threadless systems, this is to permit the bars to be raised higher.
Then you need to chose the geometry of forks which will give good handling on your bike. This is related to the angle of the headtube, which will probbaly change if you fit a non-sus fork (the front of the bike will be lowerd, and the headtube angle steepened). Forks are available with differing amounts of "rake".
If you are using forks for road-only with no serious off-road, then consider some lighter-weight forks, more like those on a touring bike. Reynolds531 steel is the standard material for touring forks, and is much more comfortable than the massive and heavy steel of most ridgid MTB forks. Usually touring forks come with mounting points for a low-rider pannier, but you can get them without if you prefer.
I would suggest you leave the job to a competant bike shop, and take a serious look at some touring-grade forks.