To maintain your list "How did you find us?" begin in the PetExec menu; Company Preferences-->Maintain How Heard.
This list is available when you add or modify an owner; "How did you find out about us?"
Want to create your own custom list? The defaults can be turned off and company specific ones added to include only the desired options. This can be accomplished by turning on the Disable Default "How Did You Find Us" Values preference and adding the desired options as shown in the previous steps.