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.
Publicly visible text/images often aren't properly deleted even when you succeed in deleting an account. Try editing or deleting them manually before deleting the account itself. If you're unsure what happens to your tracks: this can be found mostly in the Terms of Service/Privacy Policy; otherwise you can always contact MyLife and ask personally. By the way, deletion requests don't necessarily mean your data will actually be deleted (e.g. due to legal obligations).
If you signed up for MyLife using a third-party login such as Facebook or Twitter, you probably want to revoke all access from MyLife. Click the icon below to find out how.