Well I'm a big advocate of having a plan. And when I say plan, I mean something you develop for yourself, not something from someone else you follow. Only you understand you, your strengths and weaknesses.
Keep it simple calories in < calories out = weight loss
It's best to tackle both calories in and calories out if you can. I'm not a big advocate of following a specific diet plan, although MANY on here are, so you need to think about what works best for you. Regardless I highly recommend calorie counting, which is so easy with the internet now. I think that would be big for you because you'd start to see how much those cokes are killing your calories each day.
For example suppose you decide to be around 1500 calories a day to lose some weight. Well then subtract 6 cokes a day (840 calories). If you only ate 660 calories of food in day you would be super starved and dangerously unhealthy. I like to think of junk calories in terms of how much real food I have to trade for it
For me seeing my day's food translated in numbers in front of me helped me prioritize behavior changes.
Obviously the cokes are a problem for you. Only you know if you are in the minority that can cut back to an acceptable amount in your calorie plan, or in the majority that has to give up those empty calories cold turkey. I drink A LOT of diet coke so I can empathize.
Welcome and good luck!