Take it to the mechanics, where they put it on a special machine. Or you can pull the radiator, and put a water hose in the side that the water usually exits, and just let it go, but that's not always a good idea.
Determine whether you need to flush it first by using an antifreeze/coolant testing hydrometer from any car parts store. Ford recommends you change coolant every 30K or 3 years.
To flush the radiator:
1) Open radiator & engine drains, or disconnect the bottom radiator hose at the radiator outlet. Remove the upper bleed port - located on center front portion of the intake manifold. Drain all the coolant out.
2) Close all the engine drains and reconnect the hose. Fill the radiator up with water.
3) Add a can of quality radiator flush.
4) Install upper bleed port cap.
5) Idle the engine until the upper radiator hose gets hot.
6) Drain the system again
7) Repeat until the water is clear and free of scale.
8) Close all drains and connect any loose hoses. Leave the bleed port open.
9) Flush coolant recovery system with water and then leave the reservoir empty.
10) Then fill it up with a 50/50 mix of water and coolant as follows:
A. Fille radiator with coolant until it reaches the radiator filler neck seat.
B. Start the engine an allow it to idle until the thermostat open (the upper hose will get hot). Coolant will flow out of the bleed port - air has been bled from the system.
C. Turn off the engine and refill the radiator until the coolant level is at the filler neck seat. Close the bleed port.
D. Fill the engine coolant overflow tank with coolant to the FULL HOT mart, put the radiator cap back on.
11) Run the engine until normal operating temperature is reached - allowing the system to pressurize - then check for leaks.
yah i just took in my car today to get a oil change and a few other small things done and they said i need a flush and also a new air filter and a new fuel filter there goes my x-mas $$