How to properly flush coolant from the radiator.

I recently purchased a 2002 bmw 745i. I have a coolant leak and noticed that the coolant was green. The person that had it before had it for less then a month, got it repo and had put green coolant. How shoud I properly flush it

That is the million dollar question. TIS say drain radiator, get under car and remove metal brace plate under engine, and then on drivers side of block near the steering shaft is a drain plug for the block. After draining and capping plugs you are supposed to turn on the heater the max and the blower to low, and then slowly fill the expansion tank until max line. Start engine let idle for a couple minutes, top off if needed, and then close cap and drive car. The next morning before you start the car open the cap when its cold and fluid will be down a bit, top back to max and close cap. Repeat for next two days.

Thanx appreciate the help