You must have at least v1.0.4. Just copy and paste this code in your template file (index.php, loop.php, etc) :

<?php if (function_exists('get_cat_icon_lite')) echo get_cat_icon_lite();?>

You can also give it the category id. If you want to display the icon for the category id number 3, you’d do that :

<?php echo get_cat_icon_lite(3); ?>