Organizations are not set in stone. People come and go all the time, and the only thing you can do about it is be prepared for these dynamics. Loio's Team plan allows you to free up seats by removing users and adding new ones in their place.
To remove a user from your team, go to the Organization settings in the User Dashboard and open the Users tab. Pick the user from the list and press the options sign to the right of the user card.
Click Delete user and confirm your decision on the pop-up screen. After that, your Team will have a vacant seat that you can fill in by inviting a new (or the same, life is an unpredictable thing) user.
Note that if you leave the seat empty without editing your plan's number of seats, you will continue to be charged for this seat.