How do you flush the radiator on a 2003 Chevrolet Impala?

Drain the coolant either by undoing the bottom hose or using the drain cock. Then fill with water. Run the engine until it is at normal operating temp then drain again. Do this until the coolant is clean. Then refill the radiator either by the radiator cap or overflow tnk. Run until at operating temp then recheck the level and add as needed. That's it. Good luck.