So you think you’re ready to buy an Android device? There are a lot of options, and finding the right one is tricky if you don’t know what to look for. Consider these four points when picking an Android device, and you'll have no problem finding one that best suits your needs.
The android operating system has a lot of customizations; however most of the customizations require the root permission. Some android phone manufacture added few 3rd party apps to their devices. Most of the situation, these apps are in the system folder. When these pre-loaded 3rd party apps receive an update, the new version not saved on the "/system/apps/" folder, instead of that, it goes to the "data/app/" folder. So that, your phone has two apk files for the same application (older version and new version). It also decreases your internal memory free space. But we can integrate the new version into the system for save the memory.
Apart from that, some android phone manufacture added useful apps to their handsets for instance "Quick Office". Some of these apps added into the "/system/apps/" folder, and they have large size apk file. So they use big space and also we can’t move them to the external memory. If we can convert them into a system file and move to the SD card, it also save the internal memory.
However like most of the customization, this method we need the root permission,
because of it’s modify the system of our phone. So first root your device and follow these instructions.