I struggle with this also. In my case, it is Cherry Coke Zero. So, it isn't the sugar. It is the flavor and the caffeine. I have cut down on it. I had got down to just doing 2 in the morning (12 oz cans) but lately I've been creeping up again. I've been working on learning how to drink green tea as an alternative. Giving up caffeine is hard for me.
I think I just have to cold turkey it and quit drinking them since it is something that I find difficult to do in moderation.