Simply drain the system, then add a lot of distilled water to fill and let it run for a minute or so, then drain again, then simply put in 50/50 mix of ani-freeze and distilled water. I would use distilled water, it is $1.00 a gallon at CVS and you'll use maybe 2.5 gallons in a stock YJ radiator. if you simply use the tap water, you can damage to cooling system and will get a lot of calcium diposits in the cooling system.