Adjust default images in NELO theme

See:
http://erin.a-cleaner-home.com/

The theme loads the same 3 images in the bottom content boxes.

Here's the code:

--------------------------------------------------------------
<div class="itembox" id="box1">

<div class="custom-bottom-image">

<img src="http://erin.a-cleaner-home.com/wp-content/themes/wpmu-nelo/images/subimage.gif" alt="box_cat_left" />

</div>

<h2>

This is box left header</h2>

<p>

All you need to do is to visit your Custom Homepage Images tab and upload new images (you can crop them after uploading) and enter text and links to replace this text.</p>

<ul class="list">

</div>

<div class="itembox" id="box2">

<div class="custom-bottom-image">

<img src="http://erin.a-cleaner-home.com/wp-content/themes/wpmu-nelo/images/subimage.gif" alt="box_cat_center" />

</div>

<h2>

This is box center header</h2>

<p>

All you need to do is to visit your Custom Homepage Images tab and upload new images (you can crop them after uploading) and enter text and links to replace this text.</p>

<ul class="list">

</div>

<div class="itembox" id="box3">

<div class="custom-bottom-image">

<img src="http://erin.a-cleaner-home.com/wp-content/themes/wpmu-nelo/images/subimage.gif" alt="box_cat_right" />

</div>
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Obviously, it's loading a file called subimage.gif 3 times.

But I can't find where--in the source files (PHP, .html, etc.) I can edit this code? I'd like to specify 3 different image files.