Are you talking the brake rotor? If so, you have to remove the tire/wheel, 4wd hub, brake caliper, and spindle nuts. This removes the whole hub and rotor assembly. Then with a brass punch or something softer than steel, beat out the wheel studs to seperate the hub and rotor, then reverse steps to install the new rotor, adding a new wheel seal and repacking the wheel bearings. Depending on how many miles and what kind of use your truck has seen, one might think about axle u joint and trunion bearing/seal as well.
Hope it helps, need more help let us know.
Chris