CSS optimization

I’ve been reading about page speed (mine is slow: http://www.printfever.com) and one of the main suggestions out there is to optimize the CSS files.

My question is: how can I combine the CSS files into one?

Got his from an article on a blog about speed:
Wordpress and CSS
You should pay special attention to this guideline if you are using WordPress. Virtually every WordPress theme has several CSS files that are loaded.
http://www.feedthebot.com/pagespeed/optimize-css-delivery.html
http://www.feedthebot.com/pagespeed/combine-external-css.html

Please let me know how can this speed issue be resolved.
Thanks for all your help,

Daniel