Thanks txesmi, it works if I set the size at the beginning and just change the sizes, but I still wonder though, why removing and recreating doesn't work..

@EVO This approach is not viable, because it will just resize the engine window, but won't change the resolution. Thanks for your input though! (Y) Nevermind, I wasn't paying attention... Your approach totally works! Thanks! But still.. why doesn't it work separately? If I call both functions separately, I won't work again...