You can change your team size at anytime from your “Billing” page.
If you increase your team size, changes will become effective immediately and you will be billed immediately for any additional user on a prorated basis, for the time remaining in the current billing cycle.
If you decrease your team size, changes will become effective immediately and you will receive a credit for the unused portion of the current plan. You will be billed immediately for the new plan on a prorated basis, for the time remaining in your current billing cycle, minus any credit you may have.
When you decrease your team size, the most recently added members (exceeding your new team size) will be automatically deleted from your team and downgraded to the Free plan.