Be logged in, then use the deletion link. As you can read, you may also want to use their public profile remover first, which erases public information present on related sites: http://www.mylife.com/wsfy.view?type=prremover
As MyLife (formerly reunion.com) states on the deletion page: all your information will be deleted permanently. Well done.
URLS:
http://www.mylife.com
http://www.mylife.com/showDeleteAccount.do