On your purchase/subscription,will get 2 welcome emails. First one will be from ChargeBee :

In the bottom of this email you will see this:

While you are waiting for your Welcome email,we highly recommend you to log into your ChargeBee Account,where all subscription and Payment details can be found.From there you will be able to :
- See your subscription renewal date
- Pause or Cancel your subscription
- Update your Billing details and your Cards
Click to Log into your account. 

By clicking in the link above (or below) you will be transfered to that Portal,where you can use your payment email and create your account. Each time you want to make a change in your billing,login to your Portal and handle everything!