Hard part/Easy Part
Draining the tank will probably be the hard part. You will need a manual or electric fuel transfer pump to get most of the fuel out.On the 1980 vintage H30's there is a panel on the cockpit sole that can be removed to give access to the batteries and fuel tank. If you don't have the panel you will have to remove the tank through the lazarette. The tank is held down on a plywood shelf by two metal straps. You will have to cut the straps and find a method to hold the new tank in place. There was a recent discussion on this topic, so try the Archives. Replacing the plywood shelf is probably not a bad idea.