In order to upgrade your subscription plan, remember that you will have to do so from the same device you signed up on.
1. Go to “Subscription” and click on “Change Subscription Plan”.
2. Select the plan you want to switch to.
Don't forget that if you are using an Android device, Google will change your renewal date to adjust the proportionate part that has not been charged for the current period. You will therefore pay nothing until the new start date of your subscription.