You need to modify the template this was added to and change the call for the button - its title
Ok its actually th eimage you are showing. You have this in the code
Code:
<button class="button" type="button" title="Calculate Shipping" onclick="javascript
: document.forms['cartform'].submit()" style="height:40px;">
<span><span><!--Calculate Shipping<a href="" class="see-details"><img src="/skin1/images/btn-view-details.gif" /></a> --><img src="/skin1/images/btn-add-to-cart.gif" width="132" height="32" border="0"></span></span>
You want to change it to show the calcualte shipping image and not the add to cart image. Also do not use html comment in the template files to comment out smarty code - use {* code here *}