Question

describe how scientific theories can change.

Answer 1

first of all, a theory is what? a theory is a comprehensive explanation that links present observation with earlier and current ones. it must follow the scientific method. has three qualities- precise, specific, quantifiable.
A simple way of conceptualizing how a scientific theories can change is if new data that does not coincide with what the data is pointing at. i.e., if we knew that classical conditioning in behavioral psych did not have a neural base point, or that it was actually located in a different area (not the cerebellum), we might have to change the theory/alter. Richard Thompson proved this in 45+/- years of research. In 2002, he became the first to identify and map the neural circuits responsible for classical conditioning. something along those lines. just precise, specific, quantifiable data that has a strong basis to point otherwise.

Answer 2

Science is based on observation. We are always testing our hypotheses. With enough testing, we get a theory. However, theories are not set in stone. With evidence to the contrary, a theory can be modified or outright discredited (that is unlikely however). So basically, we learn something new, and we rewrite our theories. Simple as that.