Go to your home screen and follow these steps......hit menu > ADD > Widgets > scroll to Program Monitor and add it to your home screen.
Now every time you might find that your phone is slowing up or lagging behind go into that widget and across the top you have the options of Active applications, downloaded, RAM, and Storage.
The two you will use the most are Active applications and RAM.
Now back to when it slows down from responding.
In the Active applications it gives you the option to exit out of applications choose each one you want to exit out of or exit out of all of them.
Under the RAM tab, you just hit the button at the bottom that says, "Clear memory".
In most cases this will speed things up on the phone without compromising the systems apps that are needed and causing a crash like an app killer would.
If the above still doesn’t seem to work. One thing I do is hold down the power button until the phone shuts off fully. Then I restart it and then run the active app and ram cleaner as mentioned above. And that usually works and saves me from having to pull my phones silicone cover off and then doing a battery pull.
And I do add......this phone DOES NOT need an app killer installed on it. I have found that the built in Program Monitor widget works just as good if not better cause it doesn’t kill the needed apps that are running. And maintains the phone from crashing or causing errors.