That's basically gonna be in about half of the public_*.pl template files. Approximately half of them reference a standard variable from public_common.pl, and the other half use their own header. So, you'll have to change it in public_common as well as all the otehr files that have their own header. Just go through and look for any of them that have the logo image at the top and make your adjustments as necessary. The code and variables are pretty self-explanitory if you know HTML.
---Skorpion