There a lot of methods to get this done, so, If I asume that you dont have access to host panel to make a redirect in cpanel or any other host manager, you can do this:
Create a new file, or replace index.php, index.htm or index.html code for this one
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-equiv=Refresh content="0; URL=http://your-new.site">
<title>Your site</title>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<meta name="robots" content="index, follow" />
<meta name="keywords" content="" />
<meta name="description" content="" />
<title>Redirecting</title>
</head>
<body>
Redirecting to the new site...
</body>
</html>