Hi @Mandy0520 & welcome to the Community!
You can definitely change to any plan as long as you're eligible for it. If you switch to a plan that's in a lower plan category, a downgrade fee may apply. You can check out this post on how to change your plan through Fido.ca, and you can checkout our available plans here.
If you have any questions or need help, let me know and I'll send you a PM.