On line 77 to 79 you'll see the code below:

<li data-thumb="<?php echo aq_resize($gallery_img['image'],80,80,true); ?>">
<a href="<?php echo $gallery_img['image']; ?>" title="<?php echo $gallery_img['caption']; ?>" class="post-gallery" rel="gallery-group"><img src="<?php echo aq_resize($gallery_img['image'],620,420,true,true,true); ?>" /></a>
</li>

Change it to:

<li data-thumb="<?php echo aq_resize($gallery_img['image'],80,80,true); ?>">
<div class="gallery-img"><a href="<?php echo $gallery_img['image']; ?>" title="<?php echo $gallery_img['caption']; ?>" class="post-gallery" rel="gallery-group"><img src="<?php echo aq_resize($gallery_img['image'],620,420,true,true,true); ?>" /></a>
<span class="gallery-caption"><?php echo $gallery_img['caption']; ?></span></div>
</li>