Try uploading the images to your current template folder and use the following code:
<link rel="apple-touch-icon" href="<?php bloginfo('template_url'); ?>/touch-icon-iphone.png">
<link rel="apple-touch-icon" sizes="76x76" href="<?php bloginfo('template_url'); ?>/touch-icon-ipad.png">
<link rel="apple-touch-icon" sizes="120x120" href="<?php bloginfo('template_url'); ?>/touch-icon-iphone-retina.png">
<link rel="apple-touch-icon" sizes="152x152" href="<?php bloginfo('template_url'); ?>/touch-icon-ipad-retina.png">
If this doesn't work, look at the page source and click/copy&paste the url of the image(s) to see if the generated URL is available.