Ha! One I finally know! (No such thing as a dumb question around here.)

Once you've identified the process ID ('ps -aux' will get you a list of the full set of processes running on the machine), "kill [processid]", then wait. It should then be gone when you list the processes again. If it isn't, you might need to wait a few minutes and issue the kill again; if that doesn't work, "kill -9 [pid]" will get rid of a really stuck process, but you should reserve that for the stubborn ones, since it forces an exit and doesn't do a graceful shutdown.