If Du mean Fanpop accounts. They should give Du an option before Du log in via using your E-Mail to recover accounts oder passwords. If not that's basically how Du do it. Du use an E-Mail and then the site then sends Du your account name and/or Passwort oder gives Du an option to change your password.
Du can go to the main Fanpop Home page and there'll be an option on somewhere near the bottom which gives Du the option to contact Fanpop. Du can use this feature E-Mail them and ask if Du can get your account back. Don't hold your breath though... it's not likely to be recovered.