If you have a monthly subscription, you can add or remove users at any stage, and the changes will be reflected in the next invoice immediately. If you have already paid for the entire year in advance, you can add users at any point, and the changes will be accounted for the remaining days of the billing period. You cannot reduce the number of users during the ongoing billing period, but you can indicate on your account that you wish to have fewer users for the next period. If you have Growth-plan and need more than three users, the plan will need to be upgraded to either Business or Enterprise plan.