Find
// This part is the logo and forum name. You should be able to change this to whatever you want...
echo '
<img src="', $settings['images_url'], '/smflogo.gif" width="1" style="float: right;" alt="" />
<span style="font-family: Georgia, sans-serif; font-size: xx-large;">', $context['forum_name'], '</span>';
Replace
// This part is the logo and forum name. You should be able to change this to whatever you want...
echo '
<center><img src="', $settings['images_url'], '/IMAGE.GIF" align="center" /></center>';