Private Sub MaximierenToolStripMenuItem_Click(ByVal sender As System.Object, _
  ByVal e As System.EventArgs) Handles MaximierenToolStripMenuItem.Click
        If Me.MaximierenToolStripMenuItem.Checked = True Then
            Dim f As New Form1 ' deine Form
            f.WindowState = FormWindowState.Maximized  ' für Maximieren
            f.Show()
        End If
    End Sub

VB@rchiv its the Best