This article will walk you through adding and removing G Suite users.
1. Select the Services menu item, then select My Services from the drop down menu.
2. Select your G Suite service.
3. On the next page, select Upgrade/Downgrade from the left hand side Actions menu.
4. Update the number of Seats to your desired amount. Select Click to Continue to continue to the check out.
5. On the next page, choose your payment method and then continue to use the checkout as usual.
If you're purchasing new users, your G Suite purchase cap will be now increased so you can login to your Google Business Apps console and add the new user.
For a guide on adding a new user in the G Suite console, reference this Google support article.