If you would like to stop advertising a vehicle, either:
Option 1
Go to the Vehicles -> Advertising section and locate the vehicle, then disable any sales channels which are enabled.
Or Option 2
Go to the vehicle in MotorDesk, then go to the vehicle's Sales Channels section and disable any sales channels which are enabled.
If you would like to revert the vehicle to the Draft status rather than being For Sale, simply go to the vehicle in MotorDesk, then go to the vehicle's Settings section and adjust the Vehicle Status field to Draft, then save. Note, you must disable any sales channels as above before you can revert the vehicle to draft.