To add a new Team Member and designate them as a Manager, see here.
To designate an existing Team Member as a Manager, go to Account>My Team, where you'll see the Team Overview page:
The third column from the left shows each Team Member's role. To designate any Team Member as a Manager, choose Promote from the Action drop-down list in the far right-hand column.
The steps to remove a Team Member's status as a Manager, except that you will choose Demote from the Action drop-down list.
Note: When you change designate a Team Member as a Manager, or remove their Manager status, email notifications will be sent to all members of this Team, including you as Manager, as well as to the Organization Lead.