.NET 3.x Удалить/заменить элемент в xml файле - Visual Basic .NET

<?xml version="1.0" encoding="UTF-8" standalone="true"?>
<sst uniqueCount="6" count="6" xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
  <si>
      <t>sd</t>
  </si>
  <si>
      <t>ssss</t>
  </si>
  <si>
      <t>qw</t>
  </si>
  <si>
      <t>dfg</t>
  </si>
  <si>
      <t>dsd</t>
  </si>
  <si>
      <t>sdf</t>
  </si>
  </sst>

Imports System.Xml
 
Module Module1
 
    Sub Main()
        Dim stra As String = "С:\test\test1.xml"
        Dim xrw As New XmlTextReader(stra)
        Dim doc As New XmlDocument()
        doc.Load(xrw)
        xrw.Close()
 
        Dim root As XmlElement = doc.DocumentElement
        oldCd = root.SelectSingleNode("//sst/si[2]")    
        
        Dim newCd As XmlElement = doc.CreateElement("si")
        newCd.InnerXml = "<t>test</t>"
 
        root.ReplaceChild(newCd, oldCd)
 
        doc.Save(stra)
        Console.ReadKey()
    End Sub
 
End Module

mports System.Xml
 
Module Module1
 
    Sub Main()
        Dim stra As String = "С:\test\test1.xml"
        Dim xrw As New XmlTextReader(stra)
        Dim doc As New XmlDocument()
        doc.Load(xrw)
        xrw.Close()
 
        Dim root As XmlElement = doc.DocumentElement
        oldCd = root.SelectSingleNode("//sst/si[2]")    
        
        oldCd.RemoveAll()
        doc.Save(stra)
        Console.ReadKey()
    End Sub
 
End Module

xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"