Let the engine cool completely
Park on a level surface and set the parking brake
Open the hood
Place a drain pan under the radiator drain valve or lower hose
Remove the radiator cap only when the engine is cool
Open the drain valve or petcock
If there is no drain valve, loosen the lower radiator hose clamp and remove the hose
Allow the coolant to drain fully
Close the drain valve or reinstall the lower hose
Dispose of the coolant properly according to local regulations