How can I delete text inside of a picturebox

Public Class Form1
    Dim Counter As Integer
    Dim g As Graphics
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        g = PictureBox1.CreateGraphics
        Counter = 0
    End Sub

    Private Sub PictureBox1_MouseDown(sender As Object, e As EventArgs) Handles PictureBox1.MouseDown
        Dim X As Integer
        Dim Y As Integer
        Dim f As New Font("Arial", 10)
        X = Cursor.Position.X
        Y = Cursor.Position.Y
        Counter = Counter + 1
        TextBox1.Text = Counter
        If Counter = 1 Then
            g.DrawEllipse(Pens.Black, New Rectangle(X - 289, Y - 157, 20, 20))
            g.DrawString("1.", f, Brushes.Black, New Point(X - 285, Y - 155))
        End If
        If Counter = 2 Then
            g.DrawEllipse(Pens.Black, New Rectangle(X - 289, Y - 157, 20, 20))
            g.DrawString("2.", f, Brushes.Black, New Point(X - 285, Y - 155))
        End If
    End Sub
End Class