The concept of change is deeply rooted in the history of humanity whether it be the animals, the climate, or the people. Change is inevitable, especially over long periods of time, but even with numerous changes the same basic fundamentals of life still hold true. Any change in people no matter how large or minuscule can only occur within the boundaries of a human existence and those boundaries cannot be easily altered. Some boundaries are determined by nature or genetics while others are a result of upbringing and experience.
The natural boundaries placed on a human being are impossible to change no matter how much a person may want to get away from them. People need to eat, breathe, and rest and there is just no possible way for a person not to do those things. Any attempt to change these boundaries is doomed to failure and would inevitably lead to the death of the person who tries.
The boundaries determined by upbringing and experience are a bit more flexible than the natural boundaries and leave room for a person to change their behavior. The fact is these boundaries are ever changing over time but they do constrain a person enough to prevent immediate, drastic, and radical behavior change. These experience boundaries are an ever evolving learning process but as they say, "A person cannot change overnight." Making changes within these boundaries is a continuous long term struggle against previous experience but is usually most rewarding for those who succeed.
In the larger scheme of things, however, no matter how much people are able to change themselves those changes do not alter the past and that history creates another boundary that is even harder for the person to overcome. People have long memories regarding the actions of other people and most do not expect that people can change. This is not to say that if a person is able to change that their previous actions should be forgotten, but in order to truly move forward that person needs to take responsibility for their actions and accept the fact that people are going to need time before they will learn to trust that person.
The answer to the question of whether a human being can change the way they are is obviously twofold and depends on a number of factors, some of which a person has control over and some that they don't. Whether the change is good or bad depends on the individual, their strength of will, and their willingness to engage in a long, uphill battle that may or may not be successful and accepted by other people.