NOTE: This article walks you though the process in classic ASAP. For these instructions in the latest version of ASAP, see Manage a family account.
Once you're on the Family Profile Page all you need to do is click the "Edit Account" button in the upper right-hand corner. The primary contact information will become editable, and from there you can add, remove, and modify the contact information for the whole family account.
To change the Primary Contact, go to the Family Profile page (View Account) and click button under "Edit Account" called "Change Primary Contact". In the dropdown, select the new primary person.