Team members in GAIN can have access and permissions to specific brands or channels only. Removing users will also automatically adjust your monthly plan.
To remove them from the entire account because they are no longer working for your company, or simply because they might have been moved to a different department go to Manage People & Permissions.
Here just select the user you have to remove and hit Remove from Account.
Important: Only users with account owners and admins can remove other accounts. Learn more about permissions here.