To remove any of your unwanted print jobs from the printer queue, you use the lprm command. As an example, to remove all your print jobs from the stu printer:
% lprm -Pstu -a
To remove the currently active job (assuming you own it):
% lprm -Pstu
Note that quite often it is too late to remove an active job from the queue.
To remove a specific job you need the job number (get this from lpq). To remove job 1234:
% lprm -Pstu 1234