To modify an existing Team, you must have certain permissions. By default, Administrator and Manager Roles can manage it.

Note that you can not assign a new Role to an existing, previously created Team just by modifying Team data.

To assign another or new Role to a Team, you must either create a new Team Template with a specific Role or modify the Team Template you were using for creating this Team.

Be careful if you choose the last options since other Teams may be using it and you don't want to change their permissions.