If the job is still running, the job will need to be Cancelled. Once the job is cancelled, it will have a status of Aborted.
Process instances having a status of Aborted can be deleted with the Delete Process Instance job. The steps to do this are below:
1. Go to Home - Reports and Jobs - Jobs tab
2. Open the job properties for the Delete Process Instance job
3. Run the job with the following parameters:
Process Instance Status: Aborted
Finish Date From: select the Specific Date radio button and leave the date blank
Finish Date To: select the Specific Date radio button and leave the date blank
Note: If any date, including a relative date, is selected on the Finish parameters on the job, the aborted processes will not be deleted. Aborted processes have a blank finish date.