basically you can upgrade when ever you want ! the thing is if your in contract there could be fees. some contracts/plans/promotions give you the capabilty of upgrading without any fees, letting you exit early into a new contract but it depends on what plan your on
As @MRSKNOWITALL suggests it depends. What plan are you on? Leasing?
Generally though you can upgrade after 12 months has passed. Usually for $149 but Optus are currently waiving the upgrade fee.
Good advice from our regulars as usual 🙂
More info can be found here ScotishMan1: How to Upgrade Your Postpaid Phone/Tablet
Let us know what you upgrade to if you do!