A lot of people tell you they are pressed on, and tell you to put a slide hammer on it and yank it apart. The proper procedure is to remove the brake caliper, remove the axle, remove the bolts on the back side of the steering knuckle that bolt the hub wheel bearing assembly to the steering knuckle, spray some wd40 or equivelent on the wheel bearing and let it soak in if it is really tight in there. Sometimes they just come right off, and sometimes you have to get a bushing driver that is the size of the opening and smack it out from the backside, then once it's out you remove the 4 bolts that bolt the rotor to hub and slide the rotor out over the wheel bearing and put the new one in. I've had issues before where someone has put an aftermarket rotor on that didn't fit over the bearing and then you just use a press and snap the rotor in half. That is a very rare situation and you shoudn't have to deal with that.