These forums are for general discussion on WordPress, CSS and design and site feedback. Official support for StudioPress themes is offered exclusively through the My StudioPress member area. Responses in this forum are not guaranteed. Please note that this forum will require a new username, separate from the one used for My.StudioPress.
You have to change the corresponding CSS in your style.css file. A handy tool to help find which CSS selector to modify is Firebug. Without a link to the site you want to customize it's hard to give you more specifics.