The front wheel hub assembly is a single unit that bolts to the knuckle with 3 bolts. The axle shaft engages spline in it that turns the drive flange that holds the rotors and wheels.
2wd trucks have the servicable wheel bearings that hold the drive flange on the spindle. Is that what you were thinking about?
They only need to be replaced if there is play in them. Jack up a wheel and grabthe top and bottom and try to wiggle it sideways.If it moves, then you need either ball joints or new hubs. It is not that hard if you have the tools (1 7/16" socket, torque wrench capable of 175 lb-ft, 12pt 14mm socket are the special stuff you may need)
Here is how the late model Ram D44 works (from my soon to be posted hub replacement Tech article):
You can see how/where the hub assembly attaches to the knuckle
Here is the back side of the hub assebly and you can see the bolts holes to hold teh hub to the knuckle and the splines for the stub shaft
Here is the front of the hub that holds teh rotor and wheel