how to Update more then one child nodes in vb.net

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VB

Thanks in advance , what is the correct way to update more then one child nodes of a node , Here is my XML document

<?xml version="1.0"?>
<Names>
  <Name>
    <First_Name>FN 1</First_Name>
    <Middle_Name>MN 1</Middle_Name>
    <Last_Name>LN 1</Last_Name>
    <Country_Code>001</Country_Code>
    <Area_Code>
    </Area_Code>
    <Phone_No>
    </Phone_No>
    <Email_Address>mail@email.com</Email_Address>
    <Address>Address 1</Address>
  </Name>
  <Name ID="2">
    <First_Name>FN2</First_Name>
    <Middle_Name>Mn2</Middle_Name>
    <Last_Name>Ln2</Last_Name>
    <Country_Code>02</Country_Code>
    <Area_Code>002</Area_Code>
    <Phone_No>0002</Phone_No>
    <Email_Address>email@mail2.com</Email_Address>
    <Address>
    </Address>
  </Name>
  </Names>

I am able to update 1st child node but on second child node it gives error ' "Object reference not set to an instance of an object. what i
want to achieve is to update all the child nodes, any kind of help will be welcomed

Function Edit() As Boolean
        Try
            'Dim xd As New XmlDocument()
            'xd.Load(App_Path)
            'Dim nod As XmlNodeList = xd.SelectNodes("//First_Name[. = '" & txtFName.Text & "']" & "/parent::node()/First_Name")

            'If nod IsNot Nothing Then
            '    For Each node In nod
            '        'nod.Item(0).ChildNodes(0).InnerText = txtMName.Text.Trim
            '        'nod.Item(0).ChildNodes(1).InnerText = txtLName.Text.Trim
            '    Next

            'End If

            Dim xd As New XmlDocument()
            xd.Load(App_Path)
            Dim nod As XmlNode = xd.SelectSingleNode("//First_Name[. = '" & txtFName.Text & "']" & "/parent::node()/First_Name")
            If nod IsNot Nothing Then
                nod.ChildNodes(0).InnerText = "33"
                nod.ChildNodes(1).InnerText = "333"
            End If

            Edit = True
        Catch ex As Exception

            MessageBox.Show(ex.Message)
            ctlStatus.Text = "Current State : " & ex.Message.ToString
            Return False
        End Try
        Return Edit
    End Function