Welcome to the community!
It all depends on the type of plan you have, if you have a BYOD plan then you will need to change your plan to one that would allow you to finance a device.
If you are currently financing a device from Fido then you will need to pay the remaining balance before you can upgrade your phone.
I want to pay the remaining balance from my phone I'm financing currently and finance another phone. Will I still be able to have my current data talk and text plan or would I have to change that plan?