In the bottom of the screen, you can Update the plan you have, meaning you can buy additional admins, users, servers or integrations without upgrading your entire plan. Just edit the number specifying how many additional admins, users, servers or integrations you'd like to add to your plan and hit the Update button.

Removing the resources (users, servers, admins) from the CAS portal doesn't automatically remove the add-on from your plan. You need to delete the add-ons from your subscription the same way as shown above.
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