Taiwan Mobile - Upgrading Phone (Still in Contract)

I want to upgrade my Samsung Galaxy SG2 to either an S4 or an HTC One. I took my contract out in March of last year, so its still within it’s 2 year contractual period. My wife speaks Chinese but doesn’t have time to go to the place where I got tge phone to see if I can upgrade. Can anyone tell me if it is possible to upgrade before I find someone to go in with me (don’t want them to waste their time if I can’t upgrade)?

Taiwan mobile would let me upgrade when I reached 18 months out of the 24 month contract.
My new contract will run for 30 months (a new 24 month contract + the remaining 6 months of the old contract).