Advanced Task Killer (ATK) is an app that allows you to manage your phone's background tasks and free up its memory. It can be used on Android 4.4 (Kitkat) and above.

The tool is very easy to use. First, you need to check the running applications on your phone. Then, you need to select the applications you want to stop or kill. After that, you need to click the "Kill" button to stop the selected apps.

You can also set the level of the task to auto-kill. If the level is set to auto-kill 1, the tool will automatically kill the application when it is not being used.