Child navigation menu modification

I am using the Silver Light theme, http://themes.wordpress.net/columns/2-columns/4366/silver-light-01/ and would like to modify the navigation menu. Currently the child pages are displayed next to the parent. I would like to change this to make it a drop-downn style menu where the shild pages are shown when someone hovers over the parent page. Any help on this would be greatly appreciated. Thanks.