Fix width to top1, etc....

Hello¡¡¡ First of all sorry for my bad english, I'm from Spain.

I have one wuestion. I'd like to give a fix width to top1... top4, because I have put 3 modules into the template gives 33% to each one of them. I'd like to have them in fixed px, for example top1 (500px), top3 (300px) and top4 (100px), so change the percentage % for px.

Where shoud I change this???

THANKS¡¡¡¡¡