Can you explain a little more on what you want? You mean RAM, not storage, right? How much memory do you have on your phone and how much is normally used? What version of Android are you using?
I am use Android 4.1 Jelly Bean.
Actually i was asking when you run any application like game "Subwaysurf" then your mobile start working slow. after that you Kill the other app which is currently in Memory it make the mobile working well . is it right ?
For something like that, you can just click the multitasking button on your phone (the right button on a Nexus 5, double click home on an HTC One, I think hold the home button on a Galaxy S3/4) and close the app from there. That should do the trick.