This is for Ubuntu 14.10/14.04
To install Zukitwo Dark Cinnamon theme:
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install zukitwo-dark-cinnamon
To install Zukitwo Dark Gnome Shell theme:
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install zukitwo-dark-shell
To install Zukitwo theme:
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install zukitwo
To install Zukiwi theme:
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install zukiwi
Gnome Shell version
Gnome Shell version
Cinnamon version
Unity version
Source: Noobslab
To apply a theme you can use either Ubuntu-Tweak tool or Unity Tweak tool or Gnome Tweak tool. To install Ubuntu Tweak tool:
sudo apt-add-repository ppa:tualatrix/ppa
sudo apt-get update
sudo apt-get install ubuntu-tweak
To install Unity Tweak tool:
sudo apt-get update
sudo apt-get install unity-tweak-tool
To install Gnome Tweak tool:
sudo add-apt-repository ppa:gnome3-team/gnome3
sudo apt-get update
sudo apt-get install gnome-tweak-tool
Just go to applications and type in Dash search any of them and launch it.
P.S.
To change shell themes in Gnome don't forget to install gnome-shell-extensions
and enable user themes.
sudo apt-get update
sudo apt-get install gnome-shell-extensions