When canceling your subscription it will stay active until the end of the paid billing period. Then it will go to read-only mode. You can cancel with the following steps:
Go to the admin settings in the purple navigation bar at the left.
Click Plan and billing in the sidebar.
You'll land on the overview tab on the plan and billing page
Click on change plan next to your plan type.
A window pops up, you will see the plan you are currently using and the other plans you can change too. At the bottom center, you can choose to cancel your current subscription.
You can always change your mind and Undo your cancellation in change plan options before the end date of your current subscription.