You can do it through ITunes by going to Preferences and then change Import Settings. Idon't remember the exact steps, so go to the Itunes Help menu. Good Luck!
Why are you removing the pictures? Does your ning site only support audio? You can convert many files free on the web. I use freefileconvert.com. I found them in a search, but only searched because my students knew that free file conversion was available on the web. :) I have used their site many times. Large files sometimes do not go through. Student podcasts aren't usually too big. Good luck.