Yes, by making up your mind that you want to behave a certain way. You keep on checking yourself. When you catch yourself going against the behavior you wanted, admonish yourself quietly and reaffirm your determination to behave differently in the future. Eventualy, your reflexes and subconscious thought patterns will get the hang of the new approach.
Your brain is an office. Your consciousness is the boss, or king. All the thoughts that go on are the secretaries. The conscious you decides what to keep and what to throw out. When the secretaries see what kind of thoughts you act upon and accept and which thoughts are rejected and shunned, they start producing the kind that gets approved.
This works best when you toss or act upon a thought right away, but it also works in retrospect.
A Midda like Chessed is easier in the sense that it is a normal decision to help or not to help. Something like anger, that only happens when you get angry, is much harder to work on. Therefore, there has to be a bigger focus on telling yourself the correct way of thinking before scenarios, and after them, to constantly judge yourself.
Hatzlacha.