The process goes something like this:
First you drain the old fluid from the radiator and the block. Your manual will tell you exactly where the drains are.
BTW.This fluid is attractive to pets and children as it is sweet, but very toxic. It'll kill 'em if they get enough, so drain and dispose of at your local McParts store, or take it back to the dealer from whence you bought the new stuff and flushing agent.
Secondly you pre-mix the citrus flush in a gallon of water making sure it has completely dissolved. This procedure is also in the manual.
Thirdly, close the drains and open the bleeding screw/bolt. Fill the system through your reservoir a bit at a time. Start the engine, turn your heat on to max and let it come up to operating temp. Let the flush circulate through the system for 5-10 minutes after the temp gauge reads normal, ie, 80 -85 degrees Centigrade.
Fourthly, shut off engine and drain flush as in first step.
Fifthly, close radiator drain and fill through reservoir with clean water. Again start the engine and keeping the reservoir full with clean water let it circulate through the system until it is running clear from your block drain - maybe ten minutes.
Sixthly, drain radiator.
Seventhly, close block and radiator drains to proper torque, mix water (I use distilled) and anti-freeze-corrosive (I use MB's) and fill radiator through reservoir. When full start engine (Heat still at max) bleeding screw still open and keep adding mix at reservoir as the level goes down. Do this until mix begins to flow out of bleeding hole. Close bleeding screw at proper torque and let engine come up to temp. Keep an eye on reservoir level until it stabilizes at the Max line. Check for leaks and tighten leaking parts incrementally until leaking stops. If you have to exceed torque values to stop a leak, DON"T! Something else is wrong. Back out and re-torque. Breaking drains/radiators etc. can turn a simple inexpensive chore into a journey of the damned! For the next week keep an eye on the reservoir and keep adding fluid as your system burps itself.
Since I do this for all our vehicles every two years, I also replace their thermostats and radiator/reservoir caps - preventative maint. and cheap. I use OE.
Where heater core lines are readily accessible I cut in a "T" from a Prestone flush kit to facilitate the flush. Follow the directions on the kit.
Some MB's have a seperate procedure for flushing heater core. Your manual will tell you.
Also a great time to replace hoses if they need it -dry brittle-soft spongy- bulged - the usual signs.
Really a messy plebian chore. On the other hand it uses up an afternoon and gets me out of doing stuff SWMBO wants me to do that are messier and more plebian!
Happiness is a well stocked