attr btn btnej cart click code customise delete event function gif image images jquery page src

I would like to customise the cart using jquery. What event do I need to use for this? I have the following code to use as a test but this does not work:

$(function() {
$('#btn_to_cart').click(function() {
$("#btnEJ").attr("src", "/images/another_image.gif");
});
})

please delete, I have found the following page:

http://www.e-junkie.com/ej/help.custom-cart.htm