It was a little bit tricky because it’s hard to see where your slider ends and where your sidebars begin because none of them have visible borders. I could see the <div> borders with Firebug or the “Inspect Element” feature in Firefox. You can change values within these 2 features and actually see the outcome without editing files. It’s good for testing things out before you edit a file.
.featured_slider #slider_root {
height: 300px;
}
I changed the value from 400px to 300px and it worked. Just adjust it the way you want.