Go to the Finance Details Tab of the primary vehicle and right click on the trade in stock number
Take delete trade-in, remove any specification lines and vehicle costings and take save you will then be presented with the following message:
1) delete the trade in vehicle record within in Vehicle stockbooks, you may wish to untick this if you would like the vehicle stock record to remain, eg you decide to outright purchase the vehicle rather than it being traded.
2) delete the CRM record for the trade-in vehicle, you may wish to untick this as the vehicle may currently be serviced by your dealership and you wish the CRM record to remain.