Public Class Form1
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        Me.TextBox1.Text = "qöwäeürß"
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        Dim temp As String = Me.TextBox1.Text
        With temp
            temp = .Replace("ö", "oe")
            temp = .Replace("Ö", "Oe")
            temp = .Replace("ä", "ae")
            temp = .Replace("Ä", "Ae")
            temp = .Replace("ü", "ue")
            temp = .Replace("Ü", "Ue")
            temp = .Replace("ß", "ss")
        End With
        Me.TextBox1.Text = temp
    End Sub
End Class