stupid newbie question

[sifoodie]

I've inherited a web site, and am updating it -- I don't have any experience with DreamWeaver, but I've stumbled along so far. My question is this: I have a navigation bar, and I've had to increase the height and width of it to allow for new menus and items. But the background doesn't cover that new area -- how can I get it to cover the white space? The images seem to be much smaller that the original space, so I assumed they just tiled the whole area, but obviously not. The web site is
notlhydro.com

Thanks!