begin
  
  Dataset.First;
  dataset.DisableControls;
  try
    while not dataset.eof do 
    begin
      dataset.edit;
      dataset.fieldbyname('rs_cena').asFloat := dataset.Fieldbyname('Firstcena').asFloat * 1.35;
      dataset.post;
      dataset.next;
      
    end;
  finally
    dataset.enableControls;
  end; 
end.