You can change your subscription plan at any time directly in the app by going to Account > Subscription. There you'll see your current plan and the option to select a new plan. 

If you're upgrading your plan, you'll pay the difference in plan prices at the time of your update and receive your new plan credits on the date of your subscription renewal.

If you're downgrading your plan, you'll start paying the new plan price and receive your credits when your subscription renews. 

You can upgrade or downgrade your plan at any time!