First of all, before you diagnose and replace a thermostat in your vehicle's cooling system, you need to check the coolant level, drive belt and temperature gauge. To avoid any negative effects, don't drive without a thermostat. In order to replace it, you should first disconnect the battery, then drain out the cooling system, locate its housing and remove all necessary components before detaching the radiator hose and opening its cover. To accomplish this, get another thermostat which will have an o-ring seal that is well lubricated, fix back the radiator hose into position then assemble all components together again.