Do you have a comlicated program (like PhotoShop), or just a basic program (like Image Expert, etc.) ...
Easiest way is to just resize them by half ... but if you have PhotoShop or something similar, it will ask when you save it if want to save it as a low, medium, high or maixium file ... low being the smallest. Medium usually works fine for me ...
Another way is to 'crop' out all the unecessary fluff ...