You can mark a vehicle to "SOLD" status by following the steps below:
Step 1: Go to Inventory on the left menu.
Step 2: Select the desired vehicle.
Step 3: Under Status >Select Sold.
Step 4: Change the visibility to ON or OFF.
Step 5: Click on the Save button at the top right corner.

By keeping the visibility ON, the vehicle will remain on the website but with a Sold sign on top of the image.
If you decide to turn the visibility to OFF, the vehicle will no longer be present on the website.