You can upgrade your plan during the subscription period.
How do I upgrade
You can upgrade your plan by doing the following
Click on the Team Settings button for the team whose plan you want to upgrade.
From the menu in the team settings, click on "Plan".
Click the "Change Plan" button in the "Plan under contract" section of the subscription plan page.
Confirm the upgrade details, payment amount, etc. displayed on the page, and click the "Pay the usage fee" button.
Fees to be settled at the time of upgrade
At the time of upgrade, you will be charged the difference between the current plan and the upgraded plan for the remainder of your subscription period.
The fee to be paid at the time of upgrade will be displayed on the upgrade confirmation page, so please check the display on the page for details.