Q: but how can you know what a key change is or how to effeciently change a key without understanding the concept through text or reference?
A: there are no text references that can teach you how to change key and have it sound ok, unless it is a song book and you are already a great reader, in which case it might be almost as good as hearing a sound recording. the only way to confirm if a key change works is to listen to the entire thing in context and see if it works