Copy the whole directory which contain this file into the folder "libraries" inside the Arduino sketchbook folder.

You can understand the location of your sketchbook folder from the Arduino IDE clicking on File -> Preferences: the "sketchbook location" is what you are looking for.

In case you don't have an "libraries" folder there just create an empty one.


For more informations see:
 http://www.arduino.cc/en/Reference/Libraries