change phone number -> new sim card?

No you can do it from you plan without changing the sim

How to choose a random phone number

To change your phone number to a random new number:

1. Go to My Plans in your Fizz account.
2. If there is more than one plan on your account, scroll to the plan you wish to change.
3. Click on Manage and choose Change phone number.
4. Here you will see your current phone number and two options:
    

   

5. Select the middle option: Get a new number.
6. Choose a number from the list. (Click Get a new number list to refresh this list. Note that you can only refresh this list 5 times. When you refresh this list, you will not be able to go back to the previous list of numbers.)
7. Click Confirm.