Almost any parts store carries a flush kit. It will flush your whole system instead of just the radiator. They come with instructions, so it's a no brainer to do.
Drain coolant, refill with water and flush solvent. Run until the t-stat has been open for a little while. Then drain again, fill with water and pull the upper hose, while filling radiator or other end of hose with water from the hose. This will rince it out and get every last drop of old stuff out of the radiator. Then drain and refill with coolant, your done.