recording subliminal messages

Please, i need help with a project for school. I am going to record sublimial messages. I already have affermafions recorded, can someone who knows Audition well please walk me through  opening the file in Audition then changing the freequencies out of the human range of hearing?

The finished recording should be silent! There will be white-noise added later.

I look forward to your help!

Thank you-

AvaDeja