What is the name of the process that changes the instantaneous frequency of an RF wave to convey information?
Why Modulation means varying some property of an RF carrier in step with an information signal. When the property being varied is the instantaneous frequency of the carrier, the process is frequency modulation (FM); the amount of frequency shift follows the amplitude of the modulating audio. Its close cousin, phase modulation, varies the instantaneous phase and produces a similar result on the air.
Watch out Frequency conversion is the tempting one, but that is mixing a signal with a local oscillator to shift it to a new frequency, as in a superheterodyne receiver, and it carries no new information.
Modulation adds information, conversion just moves the signal. Frequency + information = FM.