You have to want to quit - cheesy saying for sure but it is a big part.
Find HELP. Whether it is AA, a counselor, therapy or rehab.
I tried to quit by myself for many years in my twenties. There was always a wedding, an event, a party, whatever - where it wasn't a "good time" to quit. That excuse will ALWAYS be there so don't use it!
Get help. It took me 2 OWIs before I was broken down enough to cry for help. Even then, it was not an easy road.