Do you mean the 'larger image' popup' If so:
Find a file called tpl_modules_main_product_image.php. It is in includes/templates/yourtemplate/templates.
Back it up somewhere safe 
Then edit it. You are looking for a line that reads:
Code:
document.write('<?php echo '<a
href="javascript:popupWindow(\\\'' .
zen_href_link(FILENAME_POPUP_IMAGE, 'pID=' .
$_GET['products_id']) . '\\\')">' .
zen_image($products_image_medium,
addslashes($products_name), MEDIUM_IMAGE_WIDTH,
MEDIUM_IMAGE_HEIGHT) . '<br /><span class="imgLink">' .
TEXT_CLICK_TO_ENLARGE . '</span></a>'; ?>');
This will take out the popup function, remove the larger image link etc
Take out bits to leave:
Code:
document.write('<?php echo
zen_image($products_image_medium,
addslashes($products_name), MEDIUM_IMAGE_WIDTH,
MEDIUM_IMAGE_HEIGHT); ?>');
If this isn't what you meant then my apologies!