Well, your oil filter is due for a change anyway, so you'd replace the oil at the same time. While the oil change is being done, why not look at getting the upper engine cleaning service? We can argue here about the best oil to use in the future, how you should drive your car, who should service it ... But if it's consuming a litre of oil every 1000 km, chances are your intake valves aren't closing properly and are in desperate need of a clean.
Thanks for the siggestion. However I just did the upper clean last service and nothing came out of my exhaust as the mechanic said it was really clean.