i want to make a change to my plan during the billing cycle, how can i do that?

Are you talking about the mobile or the residential internet?

At this time of covid, Fizz apply the modification of the residential internet in a day or two

However, you cannot modify your plan in the 48 hours before the new cycle.

this is the guide
https://fizz.ca/en/faq/i-would-like-to-change-my-fizz-home-internet-plan-how-do-i-do-this

How to change your plan:
1- Log into your account and go to Manage.
2- Click on Adjust plan.
3- Here you will be able to choose the speed that’s perfect for your needs.
4- Which speed should I choose?
5- As you adjust your plan, your new monthly fee will be displayed below.
6- When you’re happy with your adjustments and monthly fee, click Save.

Sorry mobile plan changes will only be processed at your next renewal.

Meanwhile, what do you need?

If you need additional data, other users can gift to your mobile plan (if you already pay for data plan). Otherwise, you can put money in your wallet (for pay-as-you-go services) or buy add-ons or travel add-ons if needed.

Hi Chany, your changes will only come into effect at your next bill cycle. You can go for add-ons if you need access now.

Chany,
You need to buy an add-on if you need it right now in your Fizz account..
Otherwise, If you change your mobile plan, this change will be effective at the renewal of your billing cycle.