how do i change mono to stereo on Audacity? first answer=10 points!?

ok, so... i'm gonna go into a singing contest at my school with the song - don't trust me - by 3OH!3 but i gotta sing without any vocals on the track!
so i downloaded Audacity onto my Mac book...
but when i put the song into audacity (with vocals) it keeps apearing as mono, how do i change it to stereo???
please answer step by step how to first change mono to stereo, and then how to remove vocals! first answer chosen as best!