Update is free. I checked AppStore for Singapore and yes, 1.2 version is available for download.
If you don't see "update" option neither in iTunes nor in iPhone's AppStore that probably can be for the following reason:
your ID in iTunes does not correspond to ID that you used for the purchase or you just need to login.
Check upper-right corner in iTunes, does it show right ID (email)?
If no, you need login with right ID and check new updates.
If yes and you are
really sure that this is right ID you used to buy the app, you can find GMAT ToolKit in AppStore and click "BUY". Then iTunes will say that you already own this App and it is free for your to download it.
(!) Be sure you use right ID, otherwise iTunes will process it as a new purchase. Double check all options before doing this.