Not easy, but not that hard. I drain the radiator, then start the car, remove the tank cap, wait for the thermostat to open...Oh crap it overflows making a mess, then with a few gallons of distilled water, steadily pour it in while the engine circulates it back to the radiator and out the drain. You should be running back and forth like a chicken with it's head cut off filling the tank, keeping an eye on your temp gauge, and looking at the drain until the water is clear. Engine off, drain cock closed, fill with coolant.
Sure there are other ways, like draining, filling with water, driving, draining again, and repeat until you get clear water. Takes more time. Might use the radiator flush products on the market. Don't know how effective they are.