You can change your Mobile Broadband plan (upgrade or downgrade) if you are on the SIM-only plan. If you are currently subscribed to the add-on deals contract, you can only upgrade to a higher plan.
Customer on Mobile Broadband 45 with a device contract. You may opt to upgrade to Mobile Broadband 65 or Mobile Broadband 105. Your contract will simply be carried forward without any advance payments.
Note: Your bill will be prorated based on your previous and current usage. Downgrade of plans with a device contract is not allowed. If you decide to terminate your plan during your contract tenure, you will be required to pay an early termination fee. All early termination charged are outlined here.