How do I replace image logo for live font logo ?

this is my website www.livrobrasileiro.com

Also, If I were to change the image extension from GIF to something else with more quality where in the codes I would have to make the changes for the website to recognize it before I update my new image?

thank you guys!

where in the codes I would have to make the changes
includes/languages/english/header.php

// added defines for header alt and text
  define('HEADER_ALT_TEXT', 'Powered by Zen Cart :: The Art of E-Commerce');
  define('HEADER_SALES_TEXT', 'TagLine Here');
  define('HEADER_LOGO_WIDTH', '192px');
  define('HEADER_LOGO_HEIGHT', '64px');
  define('HEADER_LOGO_IMAGE', 'logo.gif');

Right on! thank you..

where do I mess with the font size of the listing titles?

where do I mess with the font size of the listing titles?
Use "change jusiciously" in place of "mess"

These are controlled by div tag or class inb the stylesheet.css file for your template