public static void upload_sftp(String filename)
{
    String host="hostname.goeshere.com";
    String username="username";
    String password ="password";
    var workingdirectory = "./subfolder";
    String uploadFile = @"c:\\abc.txt";
    int port=22; //default value for SFTP client
    using (var client = new SftpClient(host, port, username, password))
    {
	    client.Connect();
	    if (client.IsConnected)
	    {
		    Console.WriteLine("Connected");
		    client.ChangeDirectory(workingdirectory);
		    using (var fileStream = new FileStream(uploadFile, FileMode.Open))
		    {
			    client.BufferSize = 4 * 1024;
                client.UploadFile(fileStream, filename); // if the same file name as from uploadfile -  Path.GetFileName(uploadfile)
		    }
	    }
	    else
	    {
		    Console.WriteLine("Not Connected");
	    }
    }
}