The wheel studs are pressed through both the hub and rotor to hold it all together. The ideal method of disasembly and assembly is to press the studs out and back in with a hydraulic or mechanical press.
You can also take them apart by carefully driving the studs out with a hammer and the hub and rotor should come right apart. When you put the new rotors on, you need to make sure that the mating surface between the rotor and hub is completely free of rust and debri. If anything gets between them, it will give the rotor a slight wobble while spinning and the front of the truck will shake when you apply the brakes. You can reasemble by carefully driving the studds back through both pieces or drawing them through with washers and the lugnuts.
Although the above methods will work for reasembly, I would recomend that you use a press to make sure that the rotors are on the hubs perfectly straight. Even the slightest amount of uneveness will cause the front end to shake during braking. (The same effect as a warped rotor)
Good luck with your project! B)
