I completely understand the struggle you are dealing with. For a long time in my life I was very vulgar in my speech. I even hear many people who consider themselves Christians using the Lord's name as a swear word, and using common vulgarity in their own language.
So how do you stop? Well, you have taken the first step, and that is to express the desire to stop, that you realize it is a problem. So kudos to you for that!
Next, ask yourself, "Where does this vulgar language come from?" Some people have told me it is simply a habit, patterns of speech that they have used for so long that they don't even think about what they say before they say it. I know in my own life, it certainly was a pattern, and it was much easier and faster to swear than to use other words to better explain myself. But that is just a symptom, that is not the reason. Jesus tells us what the problem is in Matthew 15:18-19 "But the things that come out of a person’s mouth come from the heart, and these defile them. 19 For out of the heart come evil thoughts—murder, adultery, sexual immorality, theft, false testimony, slander." What Jesus is saying is that what comes out of your mouth tells the condition of your heart. If your heart is full of anger, then anger comes out of your heart. If it is full of evil thoughts, then those come out of your mouth. If your heart is full of love, acceptance, and pure thoughts, then these things will flow from your heart.
The next step is to evaluate your relationship with Jesus. Do you know Jesus as Lord and Savior? If you don't, then that is the first step, and let me tell you why. When you accept Jesus as your Lord and Savior, you have not only received eternal life, the Bible tells us that you have been made new: 2 Corinthians 5:17 "Therefore, if anyone is in Christ, the new creation has come: The old has gone, the new is here!" So, given that you are a new person, you don't have to be held by the same things you were before. You are no longer a slave to your sin, you are now a new person, bought and freed by the blood of Christ. So, with that in mind, this is perhaps why you feel the need to stop cursing.
Now, if you have accepted Christ, and He is indeed your LORD, then why are you still swearing? Again, I would point to Matthew 15:18-19 above, and ask: What are you filling your heart with? Are you watching vulgar movies? Do you listen to music that has a lot of swearing in it? Do you hang around with people who are not saved who use vulgar language? If so, you need to fill your heart with the antidote--the Living Word of God.
What broke my sin of vulgarity was spending time reading the Bible, and getting a very deep understanding of His love for me. Learning how His desire for my very best meant that these bad habits had to go away, and I had to replace them with His love. Phillipians 4:8 is the key to this: "Finally, brothers and sisters, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things." By surrounding yourself in His Word--get involved in a good Bible study--you will fill your heart with His Truth. By watching less tv, listening to Christian music, and changing the people you hang around with, you will find your heart changing. And when your heart changes, the things that come out of it will change as well.
It also takes discipline, as changing anything in our lives does. Not only the discipline to change your habits, but the discipline to guard what comes out of your mouth. Proverbs 21:23 says "Those who guard their mouths and their tongues keep themselves from calamity." Hold yourself accountable to God for what comes out of your mouth, that it would bring forward love rather than rage. Psalm 19:14 prompt us "May these words of my mouth and this meditation of my heart be pleasing in your sight, Lord, my Rock and my Redeemer." Also, though, it is important to understand that you need to have grace for yourself--you will slip from time to time. Doesn't make it right to do so, but when you do, simply apologize to Jesus, and remind yourself that you are not that person anymore.
One last thing--don't go around telling all your friends that they need to stop swearing or acting like you are better than they are. It is much better to simply stop swearing. They will notice, and this may bring opportunities for you to share why and how you stopped. I did ask my co-workers in one job to refrain from using God and Jesus as swear words, as that was offensive to me--and they made solid efforts to do so, because they knew I was sincere. As you grow and change, your friends and family will notice, and that will give you chances to talk to them about the love that fills your heart.
Whew! That was a long answer to a short question--I hope there is something there that helps you! I will be praying for you that Jesus' love will so fill your heart that not only will vulgarity so offend your tongue that you won't want to use it, but that your heart will so overflow with loving words that you become a beacon of love and hope for all who know you!
If you would like to speak to me further about this or anything else, email me at firstname.lastname@example.org