doing it is quite simple.
Materials You Will Need
-water house
-1 gallon of collant
-2 empty 20oz bottles or something simlar
-bucket or oil drain pan
-collant cleaner
-possibly a set of pliers if petcock valve is tight

First you lossen and drain the coolant from the petcock valve. Next you wash your coolant system out. Close petcock pour cleaner in system and put water in till it reaches right level, run ur vechile for 5-10 minutes, drain the cleaner and water be carefull it will be hot. Next leave the pet cock valve open and wash out system some more. then take to 20oz bottle and put a bottle of coolant in and bottle of water and so on and you want to have a 50/50 mix. after you are done make ur collant bottle a 50/50 mix and throw it in the back of ur vechile incase you need to add more or you notice ur car is running at to high of temps.