How can I download all the files along with filenames that are choosen into application folder

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C#

ASP

.NET

Below is my code to convert audio files of any extension to .wav format.but what happens is if i am uploading 5 files at a time it only converts on files downloads and that file gets downloaded in my application folder or if i choose only one file for the first time it gets downloaded but without filename again if i am running the application the new file that we are taking doesn't gets downloaded.

string fileName = string.Empty;
string savePath = string.Empty;
protected void Page_Load(object sender, EventArgs e)
{

}

protected void UploadBtn_Click(object sender, EventArgs e)
{

    savePath = Server.MapPath(".") + "\\TempFiles\\";
    if (FileUpload1.HasFile)
    {
        fileName = Server.HtmlEncode(FileUpload1.FileName);
        string extension = System.IO.Path.GetExtension(fileName);

        if ((extension == ".DSS") || (extension == ".ds2") || (extension == ".dss") || (extension == ".WAV"))
        {
            ToWav(fileName, savePath);
            savePath += fileName;
            FileUpload1.SaveAs(savePath);
            UploadStatusLabel.Text = "Your file was uploaded successfully.";
        }
        else
        {
            UploadStatusLabel.Text = "Your file was not uploaded because " +
                                     "it does not have a .dss or .ds2 or .wav extension.";
        }

    }

}

static void ToWav(string filename, string path)
{
    using (DsReader dr = new DsReader(filename))
    {
        IntPtr format = dr.ReadFormat();
        using (WaveWriter ww = new WaveWriter(File.Create(path + ".wav"), AudioCompressionManager.FormatBytes(format)))
        {
            byte[] data = dr.ReadData();
            ww.WriteData(data);
        }
    }
}

What I have tried:

i had tried the above code which downloads only one file if we are selecting mutiple files also if we again run the application the file that was choosen second time doesn't gets downloaded with file names