How do I stop or reset web client downloading process

void start()
    {
        Uri source = new Uri(comboBox1.Text);
        file = source.ToString();
        button1.Text = "Stop";
        wc.OpenRead(source);
        path = comboBox2.Text;
        wc.DownloadProgressChanged += (s, z) =>
        {
            label3.Text = $"Downloaded as MB: {((float)z.BytesReceived / 1048576).ToString("#.#")}";
            label4.Text = $"Downloaded {z.ProgressPercentage}%";
            progressBar1.Value = z.ProgressPercentage;
            timer1.Start();
        };
        wc.DownloadFileAsync(source, path + Path.GetFileName(source.ToString()));
        button3.Visible = true;
    }
    void stop()
    {
        wc.CancelAsync();
        button1.Text = "Start";
    }