As the Administrator of your site and account, you have the ability to add or reduce seats.
From your Autodesk account, you can adjust the number of seats on your subscription by navigating to Billing and Orders > Subscriptions and Contracts area of your account.
After selecting Subscriptions and Contracts, select Flow Production Tracking - Subscription
Then, either select Add seats or Reduce. Remember, seats must be equal to or greater than the number of active users on your site, via the People page. You can also review more subscription details—including how many subscriptions are currently in use—from your Subscription Manager on your site.
You can add users from the People Page.
You can view and manage subscription details from the Subscription Manager.