To access the users within your account, the administrator would need to access the Altium Dashboard for your account:
From here, select the Users tab to access the Users page.
Select the <Add User> option to access the Add User's page to enter in Personal Details:
After adding the user, you can manage the profile by selecting the newly added User in the Users list to get to the Member Profile page. From here, you will get many options, one of them is to Activate / Deactivate the User:
You can also add the User to a Group by selecting the Add to the Group option: