Ask the hotel directly but my suspicion is that there is not much room to upgrade as beyond the duplex, which I think is fabulous, the next grade is suites and they don't normally upgrade to suites. Most of the regulars know to book a club standard room which then gets upgraded to a duplex.

That said there seems to be something going on if the hotel is now allowing lounge pass guests to access the full club lounge. In December all I managed was the Singaraj lounge but was upgraded to a duplex.

Whatever you get, the club experience is excellent. Enjoy