Go to System settings -> Application appearance (or Workspace appearance).
In some items (Colors, Icons, etc) you have the option to:
- Get new (you can search in a dialog box)
- Import (search a downloaded file and install it)
In other items (Style):
- If it's in the repositories: use synaptics (or similar)
- If it isn't in ther repositories: see if there's a PPA and use it
There are other situations that involve compiling a theme, but that's a longer story.
1. Download X-Aero theme
Open your terminal and run following command :
wget http://xfce-look.org/CONTENT/content-files/170901-x-aero.zip
2. Extract the theme
cd Downloads/ && unzip 170901-x-aero.zip
3. Copy all theme folder to /usr/share/themes
First, open Thunar as root :
gksudo thunar
Select all X-Aero theme folder in Downloads/
Directory
Paste it to /usr/share/themes
directory.
4. Open your theme setting
Go to Setting --> Appearance and you'll see many themes with X-Aeros name, click on one of them.
Best Answer
Open the archive and place its contents in '~/.themes'
'.themes' is located in your home folder. It's a hidden folder that you can make visible by pressing ctrl H.
If you don't have a '.themes' folder; create it.
With this method you are the only user that can use the theme. If you wish to install system-wide use the other answer.