private void button1_Click(object sender, EventArgs e)
    {
        string url = @"http://dl2.soft98.ir/soft/NET.Framework.4.5.50709.x86-x64.rar";

        // Create an instance of WebClient
        WebClient client = new WebClient();

        // Hookup DownloadFileCompleted Event
        client.DownloadFileCompleted +=
        new AsyncCompletedEventHandler(client_DownloadFileCompleted);

        // Start the download and copy the file to c:temp
        client.DownloadFileAsync(new Uri(url), @"c:frame.zip");
    }

    void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
    {
        MessageBox.Show("File downloaded");
    }

private void button1_Click(object sender, EventArgs e)
{
    string url = @"http://www.persiajonoub.net/soft/NET.Framework.4.5.50709.x86-x64.rar";

    // Create an instance of WebClient
    WebClient client = new WebClient();

    // Hookup DownloadFileCompleted Event
    client.DownloadFileCompleted +=
    new AsyncCompletedEventHandler(client_DownloadFileCompleted);

    // Start the download and copy the file to c:temp
    client.DownloadFileAsync(new Uri(url), @"c:frame.zip");
}

void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
    MessageBox.Show("File downloaded");
}