Imports System.Text.RegularExpressions 

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        TextBox2.Text = ConvertFirstTrTdToTh(TextBox1.Text.Trim)

        TextBox3.Text = ConvertFirstTrThToTd(TextBox2.Text.Trim)

    End Sub

   Public Function ConvertFirstTrTdToTh(ByVal strContent As String) As String        

　　　Dim strOld As String = strContent.Trim

        'RegexOptions.Singleline 模式下 .代替任何字符 包括回车换行        

　　Dim regexTable As New Regex("<tbody[^>]*>(.+?)</tr>", RegexOptions.Singleline) 

　　Dim regexFirstTr As New Regex("<tr[^>]*>(.+?)</tr>", RegexOptions.Singleline)        

　　Dim regexTd As New Regex("<td[^>]*>(?<tdContent>.+?)</td>", RegexOptions.Singleline)

        For Each mTable As Match In regexTable.Matches(strOld)

            Dim strFirstTr As String = regexFirstTr.Match(mTable.Value).Value

            'For Each mTd As Match In regexTd.Matches(strFirstTr)            

　　　　Dim strTdTh As String = regexTd.Replace(strFirstTr, "<th>${tdContent}</th>")            

　　　　'Next

            strOld = New Regex(strFirstTr).Replace(strOld, strTdTh, )

        Next

        ConvertFirstTrTdToTh = strOld     

End Function

    Public Function ConvertFirstTrThToTd(ByVal strContent As String) As String        

　　Dim strOld As String = strContent.Trim

      Dim regexTable As New Regex("<tbody[^>]*>(.+?)</tr>", RegexOptions.Singleline) 

　　Dim regexFirstTr As New Regex("<tr[^>]*>(.+?)</tr>", RegexOptions.Singleline)        

　　Dim regexTd As New Regex("<th[^>]*>(?<tdContent>.+?)</th>", RegexOptions.Singleline)

        For Each mTable As Match In regexTable.Matches(strOld)

            'Dim mgFirstTr As MatchCollection = regexFirstTr.Matches(mTable.Value)

            Dim strFirstTr As String = regexFirstTr.Match(mTable.Value).Value

            'For Each mTd As Match In regexTd.Matches(strFirstTr)            

Dim strTdTh As String = regexTd.Replace(strFirstTr, "<td>${tdContent}</td>")           

  'Next

            strOld = New Regex(strFirstTr).Replace(strOld, strTdTh, )

        Next

        ConvertFirstTrThToTd = strOld    

 End Function

End Class