How do I change a front wheel bearing on a 2004 gmc sierra 4x4

The hub, bearing, and ABS sensor are a single unit on this vehicle. You need to remove the wheel, brake rotor & caliper [don't disconnect the brake hose from the caliper, just support it out of the way] and then remove the large nut that holds the axle shaft in the hub assembly. Once you have all this loose or removed you'll find that the hub is held on with 3 fairly large capscrews that come in from the backside of the steering knuckle that the hub attaches too. Assembly is just the reverse of the process. Make sure you tighten all the bolts and nuts securely with a torque wrench [I don't have the torque spec's here] I apply threadlocker to all of these bolts as they are vital to safety. I only use OEM hubs on these as I've had the best luck with them and the ABS sensors inside of them.