Login to your account, and click your Organization’s Profile which will be right next to the ‘viewing as: Grantee’ section at the top. Then, navigate to the Users tab, and you will be able to see a list of associated users with your account. You can click the ‘add users’ button and then it will prompt you to enter in their email address and first and last name. If you would like to remove a user already in your organization's account, hover over the ‘Actions’ field in the table and click on the X button. It will ask you if you are sure you want to remove the user and then you can press ‘OK’ to confirm.