- Go to Setup -> Customize -> the Lookup object (Contact, Account, etc) -> Search Layouts.
- Click Edit next to Lookup Dialogs.
- Move the fields that you want in the Available Fields column to the Selected Fields.
- Click Save.
For Custom Objects (eg Tributes, Recurring Gifts, etc) edit the fields of the Lookup Dialog by doing the following:
- Go to Setup -> Create -> Objects -> the Lookup object (Tribute, Recurring Gift, etc).
- Under Search Layouts, click Edit next to Lookup Dialogs.
- Move the fields that you want in the Available Fields column to the Selected Fields.
- Click Save.