If you want to upgrade your phone, you have to pay off current tab. You can check it through self serve :Login > click "self serve" > Koodo Tab
You can add this amount to your next bill. Then you can start a new Tab. You can put $360 on the tab and you need to pay difference if the phone is over $360. $15/mo tab charge will be added to your bill until you pay off your phone.
And, don't worry about your English, I'm Japanese :)