Here is a short guide to install the Orta theme by SkiesOfAzel. To install the theme open a Terminal window and copy+paste the following lines:
sudo add-apt-repository ppa:nikount/orta-desktop
sudo apt-get update
sudo apt-get install orta-theme
When installed you can find the Orta Settings Manager under System -> Preferences -> Orta Settings Manager. Here you can make some changes to the Orta theme and to use the Orta theme select it under System -> Preferences -> Appearance.