If you don’t want to depend on any third-party apps to kill apps for you, you can simply make use of a built-in feature in android to get the same effect. The feature in question will enable you to limit the number of background processes that can run on your device. But to access the functionality, you will need to follow these necessary steps:

Enable developer options on your device by continuously tapping on the build number in the ‘About Phone’ section of the settings menu of your device

In the developer options, navigate down to the Apps section and tap on ‘Background process limit.’

Then tap on the number of background processes that you want to allow, and when that is done, it means you are all set.

You can also prevent apps from running in the background by switching on the ‘Don’t keep activities’ options in the same menu which will kill every activity as soon as you change to a different task.

However, this might not have a significant effect on the overall performance of the device as it will have to load up apps from scratch each time you access them which will take a fair share of your time.

http://www.infinix.club/ng/forum/690/850418