Launch your audio editing program and drag the recorded audio file into the main window to prepare the audio for processing.
Select "Change Tempo" or the equivalent function from your audio editing program. This function can typically be found in the "Effect" or "Audio Effect" menu.
Adjust the slider to change the tempo of the vocals to your desired speed. Use the "Preview" or "Monitor" option to listen to the new tempo. Tweak the tempo until you achieve your desired speed.
Select the "Normalize" option from the "Effect" menu, or the equivalent menu in your audio program. Leave all options at the default setting and press "OK." This will increase the volume to the maximum range without clipping. If you want the vocals to be softer, use the slider to select an appropriate percentage of the maximum volume.