Using windows Media Player (WMP) to slow down the speed of a song

Step 1:  Select a .mp3 file and open it with WMP

Step 2: With the song playing, on the top bar click 'Now Playing', then Enhancements, and finally 'Play Speed Settings'.  This will open a frame towards the bottom of the WMP window.

To play the song slower, drag the pointer currently at 1.0 to the left.  In the example below, the pointer is moved to 0.5 and the song will play at half speed. 

To return to normal speed, drag the pointer back to 1.0.  To close the speed window, click on the red X in the upper right part of the Play Speed Settings frame.