Assuming you want to switch to another carrier and bring your phone number with you, there's nothing you need to do to your account at the Public Mobile end. Just pick your new carrier and have them port (transfer) your phone number from Public Mobile (note: you'll need your account number). When the porting process has completed, your Public Mobile account will automatically be cancelled.
Do NOT take any steps to manually cancel your account first, because that will make it impossible to port your number.
