Optus are very strict about the 12 month update window for leases. Anything before that time is considered a full contract break and full fees are payable.
Note swapping at 12 months will extend your lease to another 24 months and cost $100. Note that a lease arrangement is IMO generally a very bad deal for the customer. Optus provide essentially identical non lease plans that provide much more flexability, don't require you fix or replace the phone if it is broken or lost and you get to keep it at the end of the 24 plan (The $240 discount on the lease is generally much less than the $1000 or so selling the phone would net)