Ubuntu is a very versatile operating system. You can change nearly everything in it, if you know how. All you have to do is install the Emerald Theme Manager. I will explain the steps below, pictures (As always) will follow.
1. Install the Emerald Theme Manager using
sudo apt-get install emerald
2. Go to the Beryl website using this link.
3. At the top of the site there will be a banner that has all the links, click on the one that says “Themes”.
4. Go through the themes and download the one you like, put it into your home folder.
5. Enter the Emerald Theme Manager by going to System -> Preferances -> Emerald Theme Manager.
6. Click on “Import” and select the file you downloaded (It should be a .emerald file).
7. Double click on it and it should be enabled and viola!
NOTE: Sometimes Emerald will not work, to fix this just right click on your desktop, click “New Launcher” and enter in the name field “Emerald Alternate”, and for the command field “emerald –replace”. It will put an icon on your desktop. After that create a new launcher and title it “GTK Standard” and in the command field enter “gtk-window-decorator –replace”. It will also put an icon on your desktop. If you double-click on the “Emerald Alternate”, it will go to your specified Emerald theme, if you click on “GTK Standard” it will revert back to the default theme.