Hi avinashm - with Business upgrade/award availability on SQ, you are looking for something in the 'I' fare bucket, but then it tends to be unreliable finding SQ award inventory through the usual places like ExpertFlyer and BCD Travel.
I find the best way to check, is like you would with a Qantas classic award booking, for a QF Domestic upgrade; i.e. Log in to your KrisFlyer account, and look for a Business Saver reward seat on the dates / flights you need. If it's there, then you should be able to book the eligible Y fare and upgrade right away. There's not always a need for the international upgrade lottery with SQ, like QF. If it's there to book, it's yours. If it's not, then you can book on the Waitlist and hope for the best. Like with any carrier, FF status will no doubt help.
Incidentally - there is no 'I' availability showing in EF, but I have looked at the availability through my KrisFlyer account, and there is Business Saver award availability (for 1 PAX... I didn't know what you needed) on ALL 4 direct flights from SIN-MEL on the 2nd Janauary 2018. Go get em!
Cheers,
Matt.
