That is not possible, you cannot change the URL of a hubpage (= http://...). You can only make a new hub with a different URL. But what many people do is the following: when they make a hub, they keep the URL rather generic and then they make the title whatever they want.
So when you write about red cars in austria, you can have the URL as Red-Cars-in-Austria but you can have as title: "Red Cars in Austria: Tips For Your Car Maintenance" or something like that. When you change the title afterwards, the URL will still be ok and you can change the title whenever you like, as long as the main subject stays the same.