In Night, how did Eliezer change from a boy to a man?

One way that Eliezer changes from a boy to a man is seen in his relationship with his father. 
At the start of the narrative, Eliezer has a traditional relationship with his father. Chlomo is a community leader and businessman.  He wields power in so far as he finds out information before it is made public.  When both Eliezer and his father are moved into one line in their first concentration camp, Eliezer is dependent on his father.  
However, as their time in the camps increase, Eliezer becomes more independent.  He learns how to survive and what to do in order to endure. Eliezer also must take care of his father. For example, he negotiates for additional rations and teaches him how to march properly so he will not be abused.  Towards the end of the narrative, Eliezer is told the harsh truth that fully displays his maturation:

Listen to me, kid. Don't forget that you are in a concentration camp. In this place, it is every man for himself, and you cannot think of others. Not even your father. In this place, there is no such thing as father, brother, friend. Each of us lives and dies alone... stop giving your ration of bread and soup to your old father. You cannot help him anymore.

Chlomo's condition weakens while he is in the camps.  At one point, Eliezer is forced to see his father "crying like a child" as the other prisoners take advantage of him. In this role reversal, Eliezer has become a man, while his father has become more like a child.  Being thrust in the position of having to take care of his father is one way in which Eliezer has changed.