I stuttered heavily but I am as good as stutter-free now. To overcome it I did one hour or more reading aloud daily, said affirmations and I practiced some strategies to use only at those times I was about to stutter. I used those strategies a lot for some months but now I rarely use them. By doing this I was not afraid to speak. My stuttering is slowly dissolving. I have transformed from someone who could not ask questions into someone who speak in front of groups at work and I speak at Toastmasters. For me this in combination with gradually exposing myself was the key. If you want to learn more about it you should check out Redefining Stuttering which is written by John Harrison. If you want more like a framework with concrete steps to follow you should read the stuttering book from Lee Lovett. Both books are a must-read in my opinion and will give you a lot of answers. This is hard work over a long time. However this is different for everyone so how much work and time is needed differs. My advise is to put in the hard work and beat it! Believe in yourself, trust the process and put in the hard work and you will see results.