How to upgrade and downgrade your plan
You can change your plan at any time in Settings > Account Settings > Billing > Plan Details.
Click the "Change Plan" button to select your new plan:
This will open a modal where you can select your new plan and confirm the upgrade or downgrade.
When you upgrade your plan you'll have immediate access to all of your new plan's features and you'll be charged a prorated amount for the plan. Then at the beginning of the next billing cycle you'll be charged the full amount for the new plan.
When you downgrade your plan you'll remain on your current plan through the end of the billing cycle. Then at the beginning of the next billing cycle you'll be switched to the lower plan.
Note that you can revoke your downgrade any time before the next billing cycle by clicking the "Revoke downgrade" button that appears in place of the "Change Plan" button.