Emerald Stretch theme w/ admin’s Gravatar as logo

I’m trying to change the logo on a website http://lawschool.ncaweb.net/

Seems simple, but the Emerald Stretch theme we have is set to include the admin’s Gravatar as the header logo on the upper left of the pages. The gravatar links up to an email then displays an image.
I tried changing the admins email but this had no effect.
I’d like to take out this function and just provide an image url.
Please see code below for reference to the the header logo in the header.php file.
Thanks!
Any advice appreciated.
h2o

<div id="header-logo">
        <a href="<?php bloginfo('url'); ?>" title="<?php bloginfo('name'); ?>">
          <div id="header-logo-gravatar">
            <?php $defgrav = get_bloginfo('template_directory') . '/img/gravatar_light.png'; ?>
           <?php echo get_avatar(get_bloginfo('admin_email'), '78', $defgrav); ?>