C# Can't upload files over 2GB

Question

how can I upload a file over 2GB via WebClient? Files are loaded less, everything is in order. Can anyone suggest? method POST

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            OpenFileDialog dialog = new OpenFileDialog();
            dialog.ShowDialog();
            video_url = dialog.FileName;
            WebClient client = new WebClient();

            var api = new VkApi();
            api.Authorize(new ApiAuthParams
            {
                AccessToken = "XXXXXXXXXXXXXXXXXXXXXXXXXX"
            });

            var video = api.Video.Save(new VkNet.Model.RequestParams.VideoSaveParams
            {
                GroupId = 12345678,
                IsPrivate = false,
                Repeat = false,
                NoComments = false,
                Name = "test"

            });

            client.UploadFileAsync(URI,PATHFILE);
        }