IdFTP1.Get('filename.extesion', 'destionationFolder', True, False);

procedure TfrmModulos.DownloadFile();
var
  sizeFtpFile: Integer;
begin
  TimerDescarga.enabled := True;
  barra.Enabled := True;
  sizeFtpFile:= IdFTP1.Size(cbModulosGSM.Items[cbModulosGSM.itemindex]);
  lblMessagesGSM.Caption := 'Check free disk space.';
  if FreeDiskSpace() > sizeFtpFile then
  begin
    barra.MaxValue := sizeFtpFile;// div 1024;
    IdFTP1.BeginWork(wmRead);
    Try
      IdFTP1.Get(cbModulosGSM.Items[cbModulosGSM.itemindex], ExtractFilePath(Application.ExeName) + cbModulosGSM.Items[cbModulosGSM.itemindex], True, False);
    Finally
      IdFTP1.EndWork(wmRead);
    end;
    if (FileExists(ExtractFilePath(Application.ExeName) + cbModulosGSM.Items[cbModulosGSM.itemindex])) then
    begin
       lblMessagesGSM.Caption := 'File '+cbModulosGSM.Items[cbModulosGSM.itemindex]+ ' downloaded.';
    end
    else
      lblMessagesGSM.Caption := 'Error '+cbModulosGSM.Items[cbModulosGSM.itemindex]+ '.';
  end
  else
  begin
     lblMessagesGSM.Caption := 'Hard disk full';
  end
end;