Overriding Theme's Stylesheet

Hi all,

I made a post on SO about centering the category navigation links in the header of my theme. I installed firebug and was able to find the code that needs to be changed, but I have no way of saving it without overriding my theme’s stylesheet. Is there a way to do this? I’m kind of new to WP & web-programming, so I’m hoping there’s an easy way.. like copying the entire stylesheet.php on firebug and pasting it to the stylesheet.php section in my theme editor on wordpress.

Link to my child website: http://phitlab.host22.com/wordpress/

Thanks for any help.

[duplicate: http://wordpress.org/support/topic/overriding-themes-stylesheet-1?replies=2 – topic closed]