When you disconnect a member from the workspace, that license can be reallocated to a new user. Simply send an invitation to the new person. When the new person accepts their invite, the unused license will automatically be reallocated to the new person.
Note: if there are inactive members in the workspace – i.e. someone who was in your workspace during the trial period but did not continue as a paid seat – the freed up license will be automatically transferred to the inactive member. It is a best practice to disconnect all inactive members so that they do not automatically gain access from an unused license.
If you don’t intend to fill an unused seat with a new member, be sure to reduce your seat count before the next billing cycle! Go to your User Menu > Settings > Billing and Purchasing > Billing Summary and click the Reduce Seats button to make changes.
If you do not have any unused licenses and need to invite someone new to the workspace, you need to purchase a new license.