How long do I wait before I can upgrade?

I have an iphone4 I have a plan for 2 years it runs out in June this year how long do I need to wait until I can get an iphone 5? I live in Australia if that helps

Till June when you get your upgrade, unless you buy it out right, or cancel your contract and start another one, but to cancel it you need to pay off what you owe in one big sum

Which phone carrier are you with? For most carriers, you are eligible for a hardware upgrade 6 months prior to the end of your contract. If you wish to upgrade earlier, you will have to pay an early cancellation fee.