Select "Manage Vehicles" (the icon above) on the left hand menu

Enter search criteria in the Search menu

Vehicles that match the search criteria are displayed in the list below

Select the Vehicle to view, edit and delete Vehicle information

Navigate to the Contacts pane towards the bottom of the window

Click on the three vertical dots icon on the right hand side of the screen next to the Customer that you want to make the primary contact

Select "Set as primary"