The correct answer to this open question is the following.
The changes in the structure of the society when the Aryans migrated to Ganga valley were the following.
When the Aryans arrived at Ganga Valley, the zone of the Ganges River, they impacted the society of the time by implementing changes to the region. Aryans raised cattle and produced food such as meat, milk. They were known to be fierce warriors that attacked other villages looking for treasures and food.
By 1500-1400 BC, they started to mix with the Harappan people in the Indus Valley. That is when they decided to focus on agriculture, diminished the consumption of cattle that end up being considered something sacred for them.
Aryan people learned to built irrigation canals to take advantage of the flooding of the rivers to have good soil and produce crops. That is how the Ganga Valley turned to be a fertile land that produced good crops.