I'm trying to find the wav file pitches in the hex editor, but I can't find them!
I tried changing some bytes but they just corrupted the file, then I tried changing more bytes but then it just crashed my audio program...
A wav file does not contain any pitches, at least not directly.
Pitch is the result of the amount of samples played in a time interval (sample rate), and for this reason playing an audio file
at the wrong sample rate affects the pitch (as well as speed).
If you want to play with pitches, do that with a MIDI file, that contains directly pitch data and can be edited as you said in your question.
Side note: a MIDI file does not contain any information about the timbre, but mainly the pitch and the dynamics (how loud is a sound)
To learn more about digital audio, read Fast Fourier Transform, Wikipedia
To learn more about MIDI, read MIDI, also on Wikipedia