This is great for making your own Karaoke song
Now before i start i want you to know this won't completely remove the singer, but it will do a pretty good job of it so its worth a try.
Step 1: Download Audacity
First you need to go to google.com and search Audacity.
Then click on the first result which brings you to there homepage and has a download like right there.
I use the beta version but it makes no difference for this.