1. Click Organization from the Settings drop down.
2. Click Manage Plan from the Organization Details screen.
3. Click on current Subscription Plan.
4. Click Edit Subscription.
5. Click on Add Addons.
6. Click Additional Users then Add.
7. Click the quality to add. (Options for 1-10 Additional Users) Then click on Update Subscription.
8. If there are no further changes needed, simply Close the pop up.