You may delete a listing for any reason at any time opening the respective listing as if you were going to edit it. On top of the editing form, find and click on the “Delete listing” option.
If your listing still had active time left (it was not expired), this time will not be recoverable. You will lose the days remaining and all the information on that listing. If you wish to upload a listing again, you will need to redo the process from the beginning.