How do I make an "Undo" button in Visual Basic 2008 for a user controlled graphics screen?

I'm using a PictureBox, with a DataGridView to put the x & y coordinances in. I'm using the TryParse method to record them, so they can be saved. I have not found any good examples of an "Undo" button anywhere on the 'net' for the undo button. The screen will save a line, or graphic made once applied, even if you remove it from the datagridview. In the event of a 'missed' line', where the line does not connect where it's supposed to, I need to be able to remove it. Here's a section of the code I'm using...

Public Class Form1

Dim canvas As Bitmap

Dim gfx As Graphics

Sub New()

InitializeComponent()

Me.DoubleBuffered = True

Me.FormBorderStyle = Windows.Forms.FormBorderStyle.Fixed3D

End Sub

Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

canvas = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height)

gfx = Graphics.FromImage(canvas)

Dim p As String = Application.StartupPath & "Test.txt"

Dim line As String = Nothing

If IO.File.Exists(p) Then

Using fn As New IO.StreamReader(p)

Do

line = fn.ReadLine()

If Not line = Nothing Then

Dim s() As String = Split(line, "~")

Me.DataGridView1.Rows.Add(s)

End If

Loop Until line Is Nothing

End Using

Me.DataGridView1.Rows(0).Selected = True

End If

Me.DataGridView1.Rows(0).Selected = True

PictureBox1.Image = New Bitmap(PictureBox1.Width, PictureBox1.Height)

End Sub

Private Sub Set1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Set1.Click

For Each i As DataGridViewRow In Me.DataGridView1.Rows

With i

Dim x1 As Integer = .Cells("X1").Value

Dim y1 As Integer = .Cells("Y1").Value

Dim x2 As Integer = .Cells("X2").Value

Dim y2 As Integer = .Cells("Y2").Value

Dim x11 As Integer = .Cells("X11").Value

Dim y11 As Integer = .Cells("Y11").Value

Dim x21 As Integer = .Cells("X21").Value

Dim y21 As Integer = .Cells("Y21").Value

Dim x12 As Integer = .Cells("X12").Value

Dim y12 As Integer = .Cells("Y12").Value

Dim x22 As Integer = .Cells("X22").Value

Dim y22 As Integer = .Cells("Y22").Value

Dim x13 As Integer = .Cells("X13").Value

Dim y13 As Integer = .Cells("Y13").Value

Dim x23 As Integer = .Cells("X23").Value

Dim y23 As Integer = .Cells("Y23").Value

Dim ParseResult As Boolean = True

ParseResult = ParseResult And Integer.TryParse(.Cells("X1").Value, x1)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y1").Value, y1)

ParseResult = ParseResult And Integer.TryParse(.Cells("X2").Value, x2)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y2").Value, y2)

ParseResult = ParseResult And Integer.TryParse(.Cells("X11").Value, x11)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y11").Value, y11)

ParseResult = ParseResult And Integer.TryParse(.Cells("X21").Value, x21)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y21").Value, y21)

ParseResult = ParseResult And Integer.TryParse(.Cells("X12").Value, x12)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y12").Value, y12)

ParseResult = ParseResult And Integer.TryParse(.Cells("X22").Value, x22)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y22").Value, y22)

ParseResult = ParseResult And Integer.TryParse(.Cells("X13").Value, x13)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y13").Value, y13)

ParseResult = ParseResult And Integer.TryParse(.Cells("X23").Value, x23)

ParseResult = ParseResult And Integer.TryParse(.Cells("Y23").Value, y23)

Dim MyGraphics As Graphics = Graphics.FromImage(PictureBox1.Image)

MyGraphics.DrawLine(Pens.Black, x1, y1, x2, y2)

MyGraphics.DrawEllipse(Pens.Black, x11, y11, x21, y21)

MyGraphics.DrawRectangle(Pens.Black, x12, y12, x22, y22)

MyGraphics.FillEllip