Can you upgrade only one leg of an international one-stop itinerary?

Hi all,
If flying one-way from Mebourne to London (via Singapore), does anyone know if it is possible to request an upgrade to PE/Business for only the second leg of this flight from Singapore to London? Or can you only request upgrade for both legs? I’m wanting to use points, but may not have enough for both legs, and so looking at upgrading for the longer leg. Thanks in advance if you can help answer this query.

Kind regards,


What carrier are you flying?