Launch the Google Play on your device by using the appropriate shortcut on the desktop or through the menu "Applications".
At the top of the program window, type the word "Subject". In the list of search results select any theme and then click "Free" to install. If the theme is paid, then confirm the payment by following the instructions on the screen.
Wait for installation to finish, after which you will be able to run it with a shortcut appeared on the desktop. Themes can be changed through the "Settings" - "Themes" Android.
To install themes you can use a third-party Internet resources that offer themes with the extension .apk. Find programs that interest you and download them from specialized sites. Please note that they have the extension .apk.
Connect your Galaxy device to the computer in disk drive mode using the USB cable or insert the USB device into the card reader. Move all downloaded files to your device.
Go to "Settings" - "Security" device and tick the item "Unknown sources". Also remove the tick from the "Check application".
Open the file system of your phone using any file Manager such as ES-file Explorer. If this program is installed on the device, perform the installation using Google Play.
Open the downloaded files one by one and confirm the installation. After that, go to "Settings" - "Themes" and select any displayed subject.