On modern monitors this is usually a simple operation. I did it to my dell 15" a week ago. Open the case and there [u]should[/u] be two easily accessible pots either on the mainbroad or on a daughter board. I had two like this one for this Dell, one for focus, one for brightness. Obviously you need to operate these while the monitor is on, so be careful.
If you can't find it easily, take it to a monitor repair dude. Lots cheaper than a 19" LCD.