Brake rotors are made of steel which can easily rust onto the hubs if left on a vehicle too long, even in dry climates. When it comes time to perform a brake job, you will need to remove the rotors for replacement or machining. In either case, if they are welded to the hubs with rust, removal may take a little while longer. Once the job is done, plan to remove them more often in the future to prevent having to deal with this again.
Spray penetrating oil between the rotor and hub liberally and allow it to soak in for 30 minutes to an hour, depending on how bad the rust has built up.
Put your safety glasses on and strike the rotor's hat (the center portion that the wheel studs extend through) with the dead blow hammer near the top. Rotate the rotor 90 degrees and strike it again at the top. Repeat this until the rotor comes free, or you have struck it 12 or more times. If it still won't come loose, move to Step 3.
Insert the bolt through the brake caliper bracket hole that is directly behind the rotor. Tighten the bolt until it contacts the surface of the rotor and then tighten it as far as you can with a socket wrench.
Strike the surface of the rotor with the dead blow hammer. Loosen the bolt, turn the rotor 90 degrees, and tighten the bolt down again as far as it will go. Strike the rotor again with the dead blow hammer. Continue to repeat this until the rotor comes free, which shouldn't take more than two or three more strikes if it hasn't come free already.
