Once you have the songs on your computer in the form of .wav files, as in, greatsong.wav you can open them in the ACW, Audio Chord Wizard. It takes some getting used to but it will create a Band In A Box chord sheet from the song which you can then choose a style, change the key, edit, and more much more. It won't be the exact same song but a recreation since you will choose a style as if you were creating your own song out of it.
If you just want to change the key/pitch of the songs you can use a free DAW program called
Audacity. It has a feature that allows you to change the key without changing the speed, with changing the speed or just change the speed without changing the key or pitch.
I do the same with a DAW called Reaper but there's a little more of a learning curve to using Reaper.

Does the noise in your head bother me ?