I'm pretty sure that you can't resize it after initialization, but you
could have a window size option in a settings menu, but the user would have to restart the application. Download
wrath to see what I mean. Or, you could somehow make a setup where your program would auto-close the window, and then reopen a new one with the correct size. But for that, all images and sounds would have to be re-created as well. One last thing: you maaaaaybe could try calling the window's :initialize method again... Just thought of that...
Anyway, hope this helps! ;)