Hi Max
When I change them I heat the case to about 120c in the oven (make sure its clean of oil and the missus is out first) support the case in the water pump area nd tap it out from the inside. There is a rubber seal behind the metal case which you have to force out of the way when you do this.

The metal case is very thin and pretty much impossible to remove without damaging it though so will definetely need replacing along with the rubber seal.