Is there another to change to fullscreen on the fly so to speak?

It doesn't work on windows, iirc.

SetVideoMode again.

Ok, so how would I do a SDL_SetVideoMode and leave everything else the same?

remember what you called it with last time, and send it again, only this with flags^=SDL_FULLSCREEN.

Ok, I did that but now the screen is black and nothing is displayed (there should be just a red triangle).

Never mind I fixed with a call to my function that resizes the window correctly. Thanks anway, you are always helpful (you probably dont remember me though).