how to update and save XMLNode value?

<AriaGostarInformation>
  <MenuInformation>
    <MenuNames Name="1">
      home
    </MenuNames>
    <MenuNames Name="2">
      pages
    </MenuNames>
    <MenuNames Name="3">
      blog
    </MenuNames>
    <MenuNames Name="4">
      gallery
    </MenuNames>
    <MenuNames Name="5">
      about us
    </MenuNames>
    <MenuNames Name="6">
    contact us
    </MenuNames>
    <SubMenuNames parentName="1">
      fgfgfgfgs
    </SubMenuNames>
    <SubMenuNames parentName="3">
    </SubMenuNames>
  </MenuInformation>
</AriaGostarInformation>

public XmlNodeList getXmlNodeList(string XmlNodeName)
{
    XmlDocument doc = new XmlDocument();
    doc.Load(_connection);
    XmlNodeList elemList = doc.GetElementsByTagName(XmlNodeName);
    return elemList;
}

public void updateXmlNodeWithAttribute(string XmlNodeName, string XmlAttributeName, List<string> XmlNodeAttribute, List<string> XmlNodeValue)
{
    XmlDocument xdoc = new XmlDocument();
    xdoc.Load(_connection);
    XmlNodeList xnode = getXmlNodeList(XmlNodeName);

    for (int i = 0; i < XmlNodeAttribute.Count - 1; i++)
    {
        foreach (XmlNode item in xnode)
        {
            if (item.Attributes[XmlAttributeName].Value == XmlNodeAttribute[i].ToString())
            {
                item.InnerText = XmlNodeValue[i].ToString();
            }
        }
    }

    xdoc.Save(_connection);
}

The getXmlNodeList method return Specified xmlnodelist from XML file and _connection is string xml address

This code does not throw an error, but DOES NOT update the XML node.

Please help me where is error in my code?