Hi yoyo_doremi,
The NBN plan can be changed anytime you want and there will be no plan change fee when you upgrade/downgrade it.
In case you change your plan in the middle of your current billing cycle then any unused portion will be credited to your account and will be used for future payments.
Once you have paid the initial payment which will consists of the modem shipping fee, prepayment for calls made outside included value, set up fee if you choose a no lock in contract and the first month's plan fee then the next month's fee will be the monthly plan fee for the plan you chose.
Feel free to check out the Community Articles we created that can be of great help for you!
