// This method will change the square button to a circular button by 
// creating a new circle-shaped GraphicsPath object and setting it 
// to the RoundButton objects region.
private void roundButton_Paint(object sender, 
    System.Windows.Forms.PaintEventArgs e)
{

    System.Drawing.Drawing2D.GraphicsPath buttonPath = 
        new System.Drawing.Drawing2D.GraphicsPath();

    // Set a new rectangle to the same size as the button's 
    // ClientRectangle property.
    System.Drawing.Rectangle newRectangle = roundButton.ClientRectangle;

    // Decrease the size of the rectangle.
    newRectangle.Inflate(-10, -10);
    
    // Draw the button's border.
    e.Graphics.DrawEllipse(System.Drawing.Pens.Black, newRectangle);

    // Increase the size of the rectangle to include the border.
    newRectangle.Inflate( 1,  1);

    // Create a circle within the new rectangle.
    buttonPath.AddEllipse(newRectangle);
            
    // Set the button's Region property to the newly created 
    // circle region.
    roundButton.Region = new System.Drawing.Region(buttonPath);
}