If you are wanting to do this at home.
This is the stuff. Jegs, Summit & some auto parts stores carry it.
It's aprox $ 20 per qt. You will need 2qts each time to do a good job.
Drain old coolant, do a quick flush with your hose. Pull the thermostat. Replace thermostat housing , dump your 1st 2 qt. In fill with water and drive the car for a few days, several heat cycles.
When it's cool pull the bottom hose and top hose off the radiator dump into a pan or gravel, not you concrete. You will be surprised at the amount of rusty crap that will run out.
Garden hose flush rad and engine 3 or 4 times with block drain plugs out.
Once water runs clear, put it all back together , add 2 qt of flush top off with water and drive again for a few heat cycles. Repeat flush again till clear.
Your block is now full of water so add 1 gal of pure antifreeze if you live in a cold weather state. Finish with 50/50 antifreeze,water mix.