If you no longer need all the seats on your account you can remove them from your Subscriptions Tab.
Click the three dots next to the seat you'd like to remove.
Then click 'Cancel Seat'.
Be careful not to cancel the Account Owner Seat! This will deactivate your account.
Note that Monthly User Seat Subscriptions are canceled immediately, while Annual User Seat Subscriptions are accessible until the end of the current Billing cycle when canceled.