front brake rotor

I have Sierra 3500 crew cab 4x4 full size bed 1998. I have been trlying to get the original rotors off the front. I have removed the calipers, the central axl nut and washer, but cannot remove the rotors. Have tried some hammering, but dont know the extent to which I can hit it. I am replacing both rotors, so I dont care what condition they come off in. Any suggestions will be helpful