Where i can do that 1.5.1.3?

I want to make whole default template width more narrow. (800px) I start to make samsung _banner pic 980x280 -->800x280px but i dont know where i can modify this box/sections in css or other file...and i dont know from where this value comes..-->pic is here http://a4.sphotos.ak.fbcdn.net/hphotos- ... 6709_n.jpg can enyone help me this..!?

Sorry my bad english.

You can change that in admin > extension > modules > Slideshow.