If your system is not rusted, oxidised or in any other way beat to hell - like oil in the cooling system due to headgasket failure and you had been using coolant all its life - just drain the coolant, flush the block and heater from the provided pipes behind the engine and fill it up with fresh coolant.
The best cooling system flush procedure has been described by mercedes benz in their service manuals and I use it on every brand of car if it requires a cooling system cleanup.
Their way is to use a 10% solution of citric acid in the cooling system.