People expect whales to be fish because they live in the sea. the recognition that whales are mammals requires a(n) of existing schemas.

Correct "change"

Schemas are patterns/ways of thinking or acting that helps in organising pieces of information and how it relates to each other. They can be preconceived ideas, ways of interpreting the information we receive so that generalisation is often times part of a schema. The schema in this example is whales are fish because they live in the sea. To recognise that they are mammals will require a change of that schema to another that may include that not everything that lives in the sea is fish and, therefore, that's not a definitive criterion.