Download the instrumental version of the song you wish to use. Install and open the program in which you're going to edit the song.
Import both the original version of the song and the instrumental to the program.
Place the original song on track 1 and the instrumental version on track 2.
Open the expanded view window so you can see the audio waves of both tracks closely. Line the tracks together so the sound waves are identical in both the original and the instrumental.
Use the zoom feature to make sure the audio tracks are completely identical to each other.
Click and highlight your instrumental track and right-click to bring up the "Invert" function.
Click the play button to ensure that only the vocals in the song are left and the instruments are gone.