You are free to upgrade or downgrade your subscription at any time based on your needs, including in the middle of a billing cycle.
Please note however that if you are on an Enterprise plan, you will need to reach out to your account manager or the support team to upgrade or downgrade.
Upgrading your plan
To upgrade your plan go to the Subscription section and click on the "Change" link:
Then, simply select the plan you'd like to upgrade to:
The requests left on your current premium plan will be automatically carried over for 3 months on top of the new monthly usage:
In case of a Yearly plan upgrade, all the requests left in the current yearly billing plan will be added on top of the new Yearly plan.
When you upgrade, the new subscription is applied immediately and a new monthly (or yearly) billing cycle starts over.
Downgrading your plan
From the Subscription section, click on the "Change" link, and then simply select the plan you'd like to downgrade to:
You'll be immediately downgraded to the new plan and any unused requests (from the old plan) will be carried over in an extra requests pack, valid for 3 months: