Converting Stereo files to Mono (snd)

i feel like a nube. was recording drums from records for about 2 hours, was planing to do it mono so i only attached one 1/4 wire. i didnt set the record page to "mono" in the mpc so i was only recording through one side but didnt notice. is there anyway to convert files to mono in the mpc or in the computer. if i make beats with these drums i will only be able to hear the drums on one side of the speakers until i track it, unless i listen to my beats from my mpc totaly mono which wont be a good thing. is there any solution or am igona have to just do it again properly

program sounds / option 7 / delete sounds

1.DELETE SOUND: The entire stereo sound will be deleted.
2.DELETE LEFT SIDE (CONVERT MONO): The stereo sound will be converted to mono by deleting only the left side.
3.DELETE RIGHT SIDE (CONVERT MONO): The stereo sound will be converted to mono by deleting only the right side.

in the manual p 159/160