A transformation is a dramatic change in form or appearance. An important event like getting your driver’s license, going to college, or getting married can cause a transformation in your life.
A transformation is an extreme, radical change. A simple haircut won't cause a transformation in your appearance, but if you dyed your hair purple and got a tattoo across your forehead, that would be another story. When a transformation occurs, we often use the phrase "undergo a transformation" in reference to the person or thing who has changed. So, if you do opt for the new hair color and tattoo, you will certainly have "undergone a transformation."