Hello Everybody

I have ajax code send data by GET method to php page

I want to change the send data method in the code from GET TO POST

THE CODE
Code:
function Add_Site(){
    var site_name = document.getElementById('site_name').value;
    var site_desc = document.getElementById('site_desc').value;
    var site_url = document.getElementById('site_url').value;
    
    if (site_name == "" || site_desc == "" || site_url == "") {
        document.getElementById('show_result').innerHTML = "fields is empty";
    }
    else {
        Http.onreadystatechange = function(){
            if (Http.readyState == 4) {
                document.getElementById('show_result').innerHTML = "";
                document.getElementById('show_result').innerHTML = Http.responseText;
            }
            else {
                document.getElementById('show_result').innerHTML = "";
                document.getElementById('show_result').innerHTML = "Loading";
            }
        }
        
        rand = Math.random() * 999999999;
        url = "addSite.php?site_name=" + site_name + "&site_desc=" + site_desc + "&site_url=" + site_url + "&rand=" + rand;
        Http.open("GET", url, true);
        Http.send(null);
    }
}