Being able to change your destiny is secondary to understanding destiny. If you don't have a personal definition for destiny, then you have no concept of what it is you wish to change. Destiny means different things to different people. To change your destiny, examine the different meanings people ascribe to that word.
DETERMINISM.
Some very antiquated psychologists believed that one's "destiny" was established by the time you reached puberty because of the various trauma and relationship patterns you had learned to develop in childhood. This kind of fatalistic view of one's psychological destiny got termed "determinism." If that's what you mean by destiny, then you're in luck. The latest research shows that your infancy and childhood are important determining factors in creating a personality, but that there are so many other psychological factors that go into individual personality that it's impossible to make any kind of blanket statements about destiny. But, even if you are locked into certain patterns of behavior because of your childhood, there is still good news. A Freudian psychologist will be very willing to take your money and listen to you talk. That's what passes for therapy in psychology. And, according to them, after years of therapy you may begin to understand the patterns that you create enough to be able to channel your actions into a more holistically profound manner of existence in order to create a more realized personhood. If not, well, you got all that crap about your mommy off your chest.
PRE-DESTINATION
Religiously, a paradox exists when we begin to discuss destiny. God gives us free will. That's pretty clear no matter what religion you practice. It's also pretty clear that God already knows what's going to happen to you every single day until you die and go to heaven (or wherever, in your case, I don't want to make any hasty judgments). So, which is it? Am I walking a fundamentally pre-determined path like a train on railroad tracks, or am I an agent of free choice, who determines what I will have for lunch (pastrami)? To change your destiny is not only impossible, it is veritably sacriligious. Take for example, Christianity. Saint Paul tells us that God worte our names in the book of life before the creation of the earth. Well, if you're not in the book, is there anything you can do to put your name there? Does God have a really big eraser for those people who change their destiny and decide not to be in the book? In terms of religion, the secret of life is in discovering, day to day, what your destiny is supposed to be. It's like an Existential Christmas party where you get to open up a new present every morning and discover what God had planned for you all along.
EXISTENTIALISM
If you don't believe in God, and you are a thinking and considerate person, then you're probably an existentialist. You see, the existentialist believes that the world is absurd, that it has no inherent meaning, and that. like Solomon in the book of Ecclesiastes says, "Vanity, vanity, all is vanity." In this absurd world, the absurd hero makes meaning in his own life through his choices and puts those choices into action. He is aware of his own absurdity, he understands that he is a plaything of fate and chance. And yet he DECIDES to be. He is conscious and heroic in his actions. He has mastered his will, and decides to be compassionate and to live his life with integrity. He MAKES his destiny, and he makes his own meaning.
NEW AGE
Of course, perhaps you just don't care about thinking too hard about these eternal questions much farther than how you feel. In that case, you possibly ascribe to some variation of New Age philosophy that requires you leave your intellect checked at the door so that you can accept some vague and sentimental melange of superstition and parapsychology with a light but satisfying wash of humanism. In this case, destiny means some amorphous astral magnetism that is causing your life to move in certain directions the way an aquaduct channels water. Well, if that's what you're thinking, then changing your destiny is simply a matter of understanding that it is the water that cuts the channel of the riverbed and not the riverbed that directs the water. Understand what forces are directing you to unwanted decisions and choices. Then align yourself with those forces that are moving in the desired direction. For instance, if your astral sign keeps directing you to fall in love with those selfish and arrogant Aries jerks, which you know you're going to regret because of your moon in Gemini, which makes it too easy for you to be bullied and manipulated, then you need to actively seek the Leo kind of guy who will possibly nurture your creative spirit without trampling down your will to power. In other words, look at the kind of relationships you are getting into, and then change the pattern.
All in all, though, destiny is something to be sought, not feared. Something to be pursued, not avoided. Your destiny is who you are SUPPOSED to be. If you become something other than that, then the universe is cheated of a unique and utterly original you.