I have a question about jquery.lightbox-0.5.min concerning thoumbnails?

I have a question about jquery.lightbox-0.5.min concerning thoumbnails?

I would like to increase the size of the thumbnail in lightbox?

I have it coded as far as adding it with all my images on my website with the rel=

and have this in my head of my templates

 <script type='text/javascript' src='./scripts/jquery.lightbox-0.5.min.js'></script>
 <link rel='stylesheet' type='text/css' href='css/jquery.lightbox-0.5.css' media='screen' />

</script>
        <script type='text/javascript'>
        /*<![CDATA[*/
        $('document').ready(function () {
        $(\"a[rel='lightbox']\").lightBox(); // Select all links that contains lightbox in the attribute rel
        });
        /*]]>*/
       </script>

What would I need to edit to increase the size of the thumbnail images

It works perfectly on the images when I click it but I would love to double the size of the thumbnail?

Thank you for any help