I've taken off the lug nuts but the tire won't come off?

I'm trying to change my tire and I've taken off the lug nuts and have the car jacked so that the tire is 1" off the ground but it won't come off. There appears to be a large bolt in the center of the lug nuts but the tire wrench won't fit over it and I'm not sure if it is supposed to come off, the manual doesn't say anything about it. Help?