Change Subscription Plan
After logging into your account, by default you will be on the Subscriptions tab. If you have navigated away, click the Subscriptions tab to get to the right screen. On mobile, you will click the text of the tab you are on now to bring down the menu.
Then click Edit next to the Subscription you would like to change.
Click the Product button that shows your current plan.
Choose the new value you would like to be billed at. Click Update to commit the changes.