People can suggest substitutes or "less unhealthy" versions, but at the end of the day, if you want to stop drinking it, stop drinking it. It is sugar, not heroin. You control your own actions and having a craving for something doesn't mean you have to give in to it. The only thing that will really work is to say to yourself "I am not going to drink soft drinks anymore." Mean it, do it, don't make excuses.
People will say it isn't that simple. Ignore them. It is exactly that simple.