Sheldon covers Dynamics GP 2013 SP2: Editing Vendor and Customer IDs. These items have moved from the Professional Service Tools to inside Dynamics GP with SP2.
Dynamics GP 2013 SP2: Editing Vendor and Customer IDs
Payables & ReceivablesGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.