Are you asking about stopping the running program, or are you talking about disabling the program so it never runs?
If the first, don't worry about it. Let Android manage memory and apps. It does it just fine. Contrary to popular opinion, there's no advantage, in terms of battery life, performance, or any thing else to having "empty" memory.
If the second, it depends a lot on what you use your phone for, and which carrier you're on. If this is what you want, let me know and I can probably point you to some other threads on the subject.