if you know the particular string you can just use the String.Replace function
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Label1.Text = "catatonic"
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim search As String = "ton"
Label1.Text = Label1.Text.Replace(search, "")
End Sub