Adding a user to your account as an admin is simple. Hover your mouse over the Account Settings dropdown box and select Invite / Manage users. In this page you can view who has access, and manage their permissions.

To add an individual, enter their email in the text box and click Add. You can revoke their access or delete their email at any time, by selecting the action next to their name in the User/Access screen.

Take a tour in adding account administrators here!