You can upgrade, downgrade or change plans at any time.
If you are mid your monthly cycle and need an immediate capacity upgrade, then you will be upgraded and charged for the new plan mid cycle but the credits from your original tier will NOT be carried over.
You cannot have 2 simultaneous subscriptions or varying levels of credit capacity.
How do I upgrade or downgrade?
Log in to your account. Click the gear in the top right corner of the screen to open your Workspace Settings. Then click Settings > Account > Billing.
On the Billing screen, you will see your subscription details. To upgrade, click the yellow Upgrade button in the top right, and select the new plan that you want.