Question

How does changing the wavelength alter the frequency of the wave? & How does altering frequency alter pitch?

Answer 1

For any wave, the product of (wavelength) x (frequency) is always the same number ... it's the speed of the wave.  So if you were able to change the wavelength somehow, the frequency would automatically change, in the opposite direction but by the SAME FACTOR, so that their product would stay the same.

If the frequency of a sound changes (and we're close enough to listen to it), our brain interprets that as a change of pitch, in the same direction as the frequency changed.

Answer 2

for a given type of wave in a given medium a larger frequency means a smaller wavelength