It's difficult to change completely, but just as drops of water over many years gradually erode hardened rock, so too can little changes gradually reduce or even eradicate those characteristics that one would prefer not to have. And we are not so hardened like rock. It just takes time, writing daily, self-reflection and self-address, and relentlessly studying oneself are the best way at eliminating those faults.
I'm primarily studying at how to handle pain, as it's what I'm most concerned about. I know there will be pain in death, as I've already done some "test runs" on the partial hanging method. So I'm studying how to face pain so that when the time comes I won't back out. From what I read, especially from Cicero's On Bearing Pain, one just needs patience and to constantly fill his mind with encouragement and to convince himself that soon the pain will be over, which it surely will be. One such quote of his is as follows, describing the best way to handle pain:
He will rouse himself, prepare and arm himself, to oppose pain as he would an enemy. If you inquire what arms he will provide himself with, they will be contention, encouragement, discourse with himself.
But I'm yet to be fully convinced and haven't yet managed to remove all fear of pain, which is why I know it takes a huge amount of study and practice to change our thoughts, which have been deeply imbedded within us since a young age, and particularly the fear of pain and death are innate to all of us. Though death itself I'm relatively at ease about, it's the inevitable pain that precedes it that troubles me most.
But study those faults which you feel are the most undesirable and work out ways to overcome them. There are plenty of resources about how to do that. No faults are unique to one person; what you feel you can guarantee countless others have felt before.