Coolant change?

I have no heat. The temp guage is ok. If I change the coolant would that help?

If I understand correctly that your temperature gauge is reading in the normal range, then you have a blocked hose going to or from the heater core, a shutoff valve inline with one of those lines is stuck in the closed position, or a door in your ventelating system is not working properly. Hot is hot, no matter if it is new or old antifreeze.