If you have really dirty coolant you will want to give it more flushes and/or use the prestone flush n fill kit as it is intended to flush the coolant out of the block. My coolant was really clean so this was the process I followed for a quick flush on my car.
Prestone Flush N Fill Kit
MOTORCRAFT VC1 Coolant Flush
MOTORCRAFT VC7B Gold Antifreeze
Drain coolant, remove thermostat, put o-ring back in, re-install thermostat housing without thermostat
Add flush solution + water, run 10 minutes, wait to cool, drain
Add water, run 10 minutes, wait to cool, drain
Backflush heater core, I think backflushing is better because of the way dirt accumulates on the heater core so I connect the hose to the heater core outlet and push it out the heater core inlet. To identify which is which… the heater core outlet goes down behind the back of the block and the heater core inlet connects by the intake, I connected a prestone flush n fill kit and an extra 12" of ¾" coolant hose that I picked up from the parts store, I wish I would have got a 4' piece of ¾" coolant hose so I had better way to get it into the waste jug. Don't backflush with full water pressure, I only cracked it open enough to get a full stream coming out of the exit hose. Then put everything back the way it was.
Re-install thermostat, refill system with concentrated antifreeze, the water left in the block will dilute it down to be the correct mixture. Run with cap off and keep adding until full.
After putting some miles on, check level and mixture, and adjust accordingly.