A free app for Android, by Smart Theme.
The app will help you to change the UI of your phone. If you are using the old version of the OS, then you can download the application to help you to update to the new version.
This app will provide you with a list of wallpapers and themes that you can choose from.
Once you have chosen the theme that you like, you will be able to download it. The theme will be saved to your phone. You will be able to use it on any device that you own.