Change speed arises complications

I was trying to make an action song faster, but after changing the speed, the voices singing and the instruments change pitch making the singing sound alien, can anyone help me revert the song to an original pitch?

First, I hope you can undo the speed changes or at least have the original so you can import it and start over.

Using Audacity 1.3.11 you have Effect > Change Tempo which changes the tempo (speed) of the song without changing the pitch.

http://manual.audacityteam.org/index.php?title=Change_Tempo

– Bill