You may change your mobile number by logging in to your account.
Select Manage > Number Change.
Click on the "View" button on the same row that shows the number you would like to request for a number change.
You may choose to replace your existing mobile number with a new VIVIFI number. Please note that a one-time fee of $21.40 (inclusive of GST) applies for this option.
You may also choose to replace your existing mobile number with a port-in postpaid number. There will not be any fee imposed for this option.
Please refer here for more info on mobile number porting.