The latest version (V1.2.1) of the F.Malpartida library is at
https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads
It should be installed in the sketchbook libraries which should be at C:\Users\yourName\Documents\Arduino\libraries
Remove any libraries named Liquid Crystal from the core libraries which came with the IDE at C:\Program Files (x86)\Arduino\libraries
If the constructor that you have found works, all is good.
#define I2C_ADDR 0x27
#define BACKLIGHT_PIN 3
#define En_pin 2
#define Rw_pin 1
#define Rs_pin 0
#define D4_pin 4
#define D5_pin 5
#define D6_pin 6
#define D7_pin 7
LiquidCrystal_I2C lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin,BACKLIGHT_PIN,POSITIVE);
If it doesn't, the easiest thing to do in order to find the correct constructor is run the I2CLCDGuesser sketch fund here
http://forum.arduino.cc//index.php?topic=157817.msg1235230#msg1235230