There are two methods to add an administrator to your portal. If the user already appears within the People tool, skip to the next paragraph. If they still need to be invited, select the People tool along the top toolbar and select Invite People in the center of the page. Next, enter the user's email address, enter a custom message, choose Administrators from the Invitee Group dropdown, and submit. When the user accepts the invitation they will be added as an administrator.
If the user is already a member of the portal, visit the People tool, click on the user's name, then click the Manage button under the user's basic details. This will generate a pop-up on which you should choose the Administrators group. This will instantly give the user administrative access over the portal.