How does a change in frequency or amplitude change the sound we hear?

Here, Amplitude mainly describes the intensity of sound we hear, They are directly proportional to each other. In other words, If Amplitude of the sound in greater, then you'll hear loud sound, vice-versa.

Frequency is the pitch of a sound. Change in frequency will change the pitch, and particularly for intensity, it doesn't affect loudness of the sound

Hope this helps!

This type of galaxy is an approximately ellipsoidal shape and a smooth, nearly featureless image. they are the largest single star systems, in the universe and are built by the collisions of many smaller galaxies.