Which detail explains how Esperanza must change?
O Esperanza sees her brother looking seriously at her.
O Esperanza bites her lip and looks down so she won't cry.
OMiguel says she only knows how to give orders to
servants.
O Miguel tells her that these problems are not her fault.

The detail that  explains that Esperanza must change- Miguel says she only knows how to give orders to  servants.

Explanation:

Esperanza has never done any household work.She has only seen Hortensia sweeping and now she is trying to recall.She doesn't even know how to hold a broom stick .

At this sight Miguel gets angry and takes the broom and the dustpan from Esperanza(she wants to cry but she holds her emotions as she does not want to cry in front of Miguel) and then he says to her that its not her fault as she has always given order to her servants and have never done any household work by herself

Thus the answer is

The detail that  explains that Esperanza must change- Miguel says she only knows how to give orders to  servants.

1) union forces launched a surprise attack.

2) more confederate troops arrived by train.

3) union forces retreated.