What kind of wheels are you trying to mount on the car? As far as removing the front wheels, If you don't care what happens to the origionals, take a cutter and cut them off the pin, then pull the pin out with pliers (heating the pin helps)
For the rears, I would just cut them off. I don't recommend heat because it can damage the axle gear or warp it.
I have a tutorial on mounting modifier rims to a bit. check it out and see if it helps
If you need to enlarge the holes in the front wheels, take a thick needle or a small dowel and heat it up . The best way would be a small drill bit. Take the tires off the rims and hold them with a pair of pliers. Make sure to go slow and hold the drill straight down.
modifier wheel tutorial