Make sure your cars engine is not really hot, cuz you dont want the coolant spraying out all over the place.

1. Release the radiator cap.
2. Open the Petcock at the bottom of the radiator and let the radiator fluid drip out into a pan.
3. Once completely drained turn on a hose and start to fill the radiator with water.
4. The water will run out of the petcock.
5. While still running the water through the radiator keeping the fluid just below the top have someone start the car.
6. Run the car for a while until all of the fluid coming out from the petcock is no longer green.
7. Once fluid is clear turn off engine and let water drain completely.
8. Shut the petcock and add a 50-50 anifreeze/water mixture.
9. Replace the radiator cap.

It isnt that hard, hope that helps.