Code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Net;


namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            webBrowser1.Navigate(textBox1.Text);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            timer1.Enabled = true;
            timer1.Interval = 5000;
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            File.Delete("C:\\Documents and Settings\\....\\Cookies\\....");
            webBrowser1.Refresh();
        }
    }
}