It's impossible. A few years ago I manually went through and "deleted" all content. It probably took me five or six hours all told. A year or so later someone was showing me something on their profile, and I noticed a picture that I thought was gone. Digging around, everything I marked for deletion had re-appeared publicly. I've since "deactivated" my account (there's no apparent way to actually delete it) and refuse to use the service, much to my family's chagrin.

tl;dr: Even if you delete things, they will eventually reappear.