You can get software that cuts the frequencies usually filled by vocals if you want to cancel them out, but you can't extract individual tracks from a song without the master copy, which (I'm guessing!) you don't have.
If this is for vocal practise and you're serious about it, you could download a MIDI file and then real-ize it with some plugins and a sequencer so you can sing along.
However if this is just to show the world on YouTube how f*cking fantastic you are then I wouldn't bother. Actually if it's for that, then just throw away your computer and cut off your internet connection. Trust me, you're doing yourself a favour.