The account holder can do this through Account Management. Login to Account Management and select Trading Access, then click on Trading Configuration. From the Account Configuration/Trading Configuration page, the account holder can select the permissions they wish to obtain. Once they have selected all pertinent permissions the account holder can submit the request.
If the account holder also wants to subscribe for Market Data which applies to those new permissions, they can also do this from Account Management by again selecting Trading Access, then clicking on Market Data Subscriptions.