const string host = "domainna.me";
const string username = "chucknorris";
const string password = "norrischuck";
const string workingdirectory = "/highway/hell";
const string uploadfile = @"c:\yourfilegoeshere.txt";

Console.WriteLine("Creating client and connecting");
using (var client = new SftpClient(host, port, username, password))
{
    client.Connect();
    Console.WriteLine("Connected to {0}", host);

    client.ChangeDirectory(workingdirectory);
    Console.WriteLine("Changed directory to {0}", workingdirectory);

    var listDirectory = client.ListDirectory(workingdirectory);
    Console.WriteLine("Listing directory:");
    foreach (var fi in listDirectory)
    {
        Console.WriteLine(" - " + fi.Name);
    }

    using (var fileStream = new FileStream(uploadfile, FileMode.Open))
    {
        Console.WriteLine("Uploading {0} ({1:N0} bytes)", uploadfile, fileStream.Length);
        client.BufferSize = 4 * 1024; // bypass Payload error large files
        client.UploadFile(fileStream, Path.GetFileName(uploadfile));
    }
}