Only about half of the 16GB internal memory is available for users out of the box. That leaves about 8GB for all the photos, music, apps and games. Considering some of the games take up over 1GB alone, internal memory can quickly run out on the Galaxy S4.
The good news is that Galaxy S4 comes with a microSD card slot that can add up to 64GB of memory. The microSD is meant for users to save all their personal files, such as photos and music files. All the apps and games are installed on the internal memory card on a standard device.
How to Install and Run Apps/Games From microSD Memory Card
The apps organizes all the apps currently installed on your device, and it will identify the apps that is capable of running from microSD card. It will then give you the option to move the apps to the memory card while maintaining the shortcuts to the Manage Applications screen.
AppMgr is also a great way to keep track of your apps and quickly identify the apps taking up large amount of memory. It has a simple interface, and works for devices with Android version 2.2 and higher.
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Tweak Your Android Device to Install on Memory Card.
If you are technically savvy and willing to make some tweaks to your Android device, there is a way to automatically install and run apps directly from your memory card. This method works for devices with Android version 2.2 and higher, does not require root access, and should work for both from your Windows and Mac computer. The process is reversible if you decide to revert back to default settings.
Steps to change your default installation folder can be found on instrutables.com.