Download Audacity. Audacity is a free music editing program you will need to convert your music from stereo to mono. Once you download Audacity, install it on your hard drive.
Run Audacity and import the music you want to convert. To do this, click on "File" and select "Open." Then select the file you want to convert to mono. Make sure the file you are converting is already in stereo.
Look at the box that appears after you import your file. You should see blue waveforms. To the left of the waveforms, you will see a bunch of numbers and other settings in a box. In the top left corner of the box, locate the arrow (which is to the left of the 1.0 number).
Click the arrow and select "Split Stereo Track" from the drop-down menu. Now you will notice that track has been split into left and right channels that you can control.
Click the arrow by the top (Left channel) waveform (this will also be to the left of top waveform's 1.0 marking). Select "mono" from the drop-down menu.
Click on the lower (Right channel) arrow. This will be located to the left of the lower waveform's 1.0 marking. Select "mono" from the drop-down menu. At this point, the boxes to the left of the top and bottom waveforms should both say "mono." If either still says "right" or "left," ensure that you followed the above steps and switched each channel to mono in the drop-down menu.
Export your now mono song by clicking on the File tab and selecting one of the export options. Choose the directory you want to export the file to and you're done.