XmlDocument xdoc = new XmlDocument();
        string val = "~/MyFiles/myxmlfile.xml";
        string path = Server.MapPath(val);
        string to = path.Replace("myxmlfile.xml", "myxmlfilenew.txt");
        StreamWriter stream = new StreamWriter(to, false, System.Text.Encoding.Default);
        xdoc.Load(path);
        xdoc.Save(stream);