Updating a Record basedon ItemID using SharePoint default WebService

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using PrasadBolla3;
using System.Xml;

public partial class Default8 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}

protected void btnUpdate_Click(object sender, EventArgs e)
{
string strUpdateCommand = string.Empty;
strUpdateCommand = "" + ddlItemID.SelectedItem.Value +"" + txtUserName.Text + "" + txtPassWord.Text + "";
PrasadBolla3.Lists objLogin = new PrasadBolla3.Lists();
objLogin.Credentials = new System.Net.NetworkCredential("true_indian9000", "prasad1234", "apptix");
objLogin.Url = "http://prasad.bolla3.sharepointsite.net/_vti_bin/Lists.asmx";
string strListName = "Login";
XmlDocument xmlDoc = new System.Xml.XmlDocument();

System.Xml.XmlElement elBatch = xmlDoc.CreateElement("Batch");

elBatch.SetAttribute("OnError", "Continue");

elBatch.SetAttribute("ListVersion", "1");

elBatch.InnerXml = strUpdateCommand;

XmlNode ndReturn = objLogin.UpdateListItems(strListName, elBatch);

string result = ndReturn.OuterXml.ToString();
txtUserName.Text = "";
txtPassWord.Text = "";
txtUserName.Focus();
}
}