Upgrades (and downgrades) are done through our Control Panel’s upgrade page.
Upgrades will take effect as soon as you go through checkout. You’re then able to make use of the extra storage, dynamic requests, production environments, and/or PHP memory limit immediately!
Downgrades are a bit different. As soon as you downgrade, the new limit for a specific item will not change immediately. It will stay the same until a new billing cycle begins. If you for example have a monthly paid plan, the newly configured plan will take effect as soon as the current month is over.
Specifications of what happens with regards to financial transactions during up- and downgrades will be visible to you during the checkout process. If you want to know more about how our billing works, we have made an article for just that.