Why delete a job when you can just close it? You have lots of space in iCat!
However, if you really need to delete a job, follow the instructions on this video which will show you how to first close a job, and then delete it.
Close the Job
2. Delete the Job using the Jobs View.
Search in the Jobs View by closed jobs.
Select the checkbox of the closed job and then select <Delete> from the Action Menu.