Install and initiate your audio editing program. Drag the audio file you would like to modify into the main editing pane. This will import your file and prepare it for editing. The editing pane typically has numbers at the top, like a ruler, that indicate where each second falls in the piece.
Select the entire audio file by double-clicking the imported wave file. The entire audio file should change color to indicate that you have highlighted it. You may also select the "Edit" menu and then click on the "Select All" option.
Open the "Effect" drop-down menu and select "Change Tempo." If you know the beats per minute of the current song, enter that number into the first box under the option "Beats Per Minute" then enter the new value in the second box. If you don't know the beats per minute of the song, use the slider option to change the tempo by a percentage.