this web service running properly individually but but when i am calling this through JSON it not reflecting the database please help me

Revision 2
How Can i call this web method through json query and how can i pass value of controls in json method to call web method and how can i show alert box on the bases of returning value from web?

[WebMethod]
    public string ChangePass(string UserName,string AltEmail,string OldPass,string NewPass,string ComfPass)
    {
        SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["Connect"].ConnectionString);
        SqlDataAdapter sp = new SqlDataAdapter("select Password from User_Registration where Password='" + OldPass + "'", con);
        DataSet ds = new DataSet();
        sp.Fill(ds);
        if (ds.Tables[0].Rows.Count != 0)
        {
            SqlDataAdapter dap = new SqlDataAdapter("update User_Registration set Password='" + ComfPass + "' where Email_Id='" + UserName + "'", con);
            DataSet ds1 = new DataSet();
            dap.Fill(ds1);
            MailMessage mail = new MailMessage("tech@xyz.com", AltEmail);
            mail.Body = "Email:-" + mail.From + "<br />" + "New Password:-" + ComfPass;
            mail.IsBodyHtml = true;
            SmtpClient smtp = new SmtpClient();
            smtp.Host = "smtp.gmail.com";
            smtp.EnableSsl = true;
            NetworkCredential NetCre = new NetworkCredential();
            NetCre.UserName = "tech@xyz.com";
            NetCre.Password = "abc@123";
            smtp.UseDefaultCredentials = true;
            smtp.Credentials = NetCre;
            smtp.Port = 587;
            smtp.Send(mail);
           return "Password change Successfully";
        }
       return "Please enter valid old password";
    }

JSON CODE:-


<script type="text/javascript" src="http://ajax.microsoft.com/ajax/jquery/jquery-1.4.2.min.js">
function changPass() {
try {
alert("ok");
$.ajax({
type: "POST",
url: "http://localhost:12345/WebSite5/ADO.asmx/ChangePassword",
data: "{'UserName':'" + $("txtUserName").val() + "', "
+ "'AltEmail':'" + $("txtAltEmail").val() + "',"
+ "'OldPass':'" + $("txtOldPass").val() + "',"
+ "'NewPass':'" + $("txtNewPass").val() + "',"
+ "'ConfPass':'" + $("txtConfirmPass").val() + "'}",
dataType: "json",
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function() { alert("Password Update Successfully"); },
failure: function() { alert("Please Enter Correct Old Password!"); }


});
} catch (e) {
alert(e);
}
}
</script>