If you print a job and then decide you want to cancel your job, use the lpq command above to get a job control number. The number you want is in the Job column. Find the jobs that are yours, and use the lprm command to kill them.
For example, if you were the user bplecs, you would type:
lprm -P ps4c 944
To cancel your job.
Note that ps4c is the queue listed above, so this would be the best queue to specify. However, ps4 would also be acceptable, since ps4 includes all of the ps4 printers.