Navigate to Pricing page.
Click on "Upgrade" or "Downgrade" depending on desired plan.
You will be redirected to stripe billing page.
Click on the "Confirm" button.
Confirm payment for Upgrades - Upgrades will require you to pay the difference in price between plans, prorated by the time left in the billing cycle (time left until the next full invoice for your new plan).
Note: If you downgrade to a plan with a lower project limit than the number of projects you currently have, projects over the new plan's limit are not deleted — they become inactive (read-only). You can choose which projects to keep active and reactivate the others later, for example if you upgrade again.