You can also use an app like
System Panel (the free version will work fine for this).
The app will open to a screen listing "running" (remember - in android 'running' does not necessarily mean it is consuming cpu) and "inactive" apps. Look for AppLauncher (it may be in either list depending on when you last launched 'Extras', but should be up at the top of either list since default is alphabetical sort). Tap it. Then tap 'End Task'.
That's it.
Almost any app that will let you list and kill running tasks will work. System Panel is a good choice since it intentionally does not include an auto-killer and is a good solid program.