Help with concentric circles

Question

Hello, so i need help. I'm a total newbie and i need help to delete every previous circle when the new one pops up.  

The program down below creates concentric circles only, and i don't know how to "recreate" it(soz, english is not my main language)

Thanks in advance. 

 

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

namespace WindowsFormsApplication1

{

public partial class Form1 : Form

{

public Form1()

{

InitializeComponent();

}

int x, y, R, d, br, pR;

Random r = new Random();

Pen olovka = new Pen(Color.Red, 5);

private void timer1_Tick(object sender, EventArgs e)

{

br++;

Graphics g = CreateGraphics();

g.DrawEllipse(olovka, x - R, y - R, 2 * R, 2 * R);

R += pR;

pR += 5;

timer1.Interval += 200;

if (br % 2 == 0) d--;

olovka.Width = d;

if (d == 0)

timer1.Enabled = false;

}

private void Form1_MouseDown(object sender, MouseEventArgs e)

{

x=e.X;

y=e.Y;

R=5;

d=5;

pR=1;

olovka.Width=d;

timer1.Enabled=true;

timer1.Interval=1;

Refresh();

br=0;

}

}

}