Download and install Audacity Music Editor software if you don't have it already (see resources below). It's free. Open the program once it has been installed.
Click "Project" from the toolbar to bring up a drop-down menu. Select "Import Audio" to open a pop-up browser window. Find the MP3 that you want to convert, and double-click it to open.
Click the downward black triangle to the left of your track to select a drop-down menu, and then choose "Split Stereo Track."
Highlight the bottom track by clicking in an empty space on the track tab, and then select "Effect" from the toolbar menu. Choose "Invert" from the drop-down menu and wait for a moment for the process to be completed.
Click the black downward triangle (the same one you clicked in a previous step) to the left of your top track. Select "Mono" from the drop-down menu. Repeat this process for the bottom track. Press the "Play" button to preview the track. It should no longer have any lead vocals on it.
Click "Edit" from the toolbar menu, followed by "Select All."
Click "File," then "Export as WAV." Save the file to your Desktop. You can now burn this track to a CD and play it in any CD player.