below i code that i am using

 var $j = jQuery.noConflict();


$j(document).ready(function(){
    $j( "#stone_theme" ).change(function() {
            new Ajax.Request("http://localhost/infoz/test.php", {
                method: 'Post',
                parameters: {"parameter_name":"value"},
                onComplete: function(transport) {
                    alert(transport.responseText);
                }
            });
    });
});