A couple of comments:
hacking the CSS (at least for something as ‘integrated’ as this slider) is not always a matter of changing a few classes & attributed).
As an earlier post pointed out, the slider part of this theme is based on a broader (non-wordpress) web template. This means that tweaking the classes and attributes may have unintended (or no) affects.
That being said, for those wanting to really tweak this theme… I recommend one of these two approaches (or both):
1.really dive into using “firebug” (or some other similar tool) so you can see ALL of the CSS classes being used for the slider.
2.and/or modifying your images, as one recent poster stated, using any number of simple image editing tools.
Personally, I’m doing a little bit of both.