UploadFile with POST values by WebClient

I want to upload file to a host by using WebClient class. I also want to pass some values which should be displayed in the $_POST array on the server part (PHP). I want to do it by one connect

I've used code bellow

using (WebClient wc = new WebClient())
{
    wc.Encoding = Encoding.UTF8;
    NameValueCollection values = new NameValueCollection();
    values.Add("client", "VIP");
    values.Add("name", "John Doe"); 
    wc.QueryString = values; // this displayes in $_GET
    byte[] ans= wc.UploadFile(address, dumpPath);
}

If i've used QueryString property, the values displayed in $_GET array.But i want to send it by post method