in order to help, you will need to provide more info,
cannot means
1) Can download audacity, can install, using the same vst(effect) in the tutorial, but unable to change the key/lower pitch
or
2) Can download everything, but dont know how to use
or
3) Cant download, cant use
Anyway, to change the pitch of audio track, there is no straight magic effect which doesnt affect the original audio files. Even if there are software to do it, will need to pay for it. What bro blurprint suggested, is prolly the best that you can try now. If theres any problem in using the software, do read through the manual and see if it helps. If not, it will be very hard for others to help/suggest.