Thanks for all your suggestion ladies. I have confirmed with the local tiffany's store manager and yes our Singapore boutiques don't do upgrades. I'm not really attached to things and my DH has agreed to trade in the original e-ring if other jewelers can give us a good price for it. I'll go around to find out which jeweler can offer me the best. If not, I'll just get another piece of jewelry for our anniversary.
I am shocked. I always thought Tiffany would do an E-ring upgrade regardless of where you bought your ring. Good luck with your eventual decision and do please post your new piece!