Is there a way to separate instrument parts from songs to listen to them by themselves?

I was trying to learn songs by ear (for keyboard) and in some of them,
they are too quiet to figure out. I thought it would be easier to take
the part out and listen to the keyboard by itself. Or if I could take
out all the other instruments, or just turn up the keyboard parts.
Does anyone know how to do any of these things? If anyone knows
another way, please tell me.
I know that you can change the equalizer in iTunes but it isn't really
helpful.