Deleting user account doesn't work

I bought a new iMac, updated it to Mavericks. Then tried to upload my old data from the backup disk onto it. I've ended up with three user accounts (1) - the one I created when I started up the new iMac, it has no files on it, I only used it for browing the internet (2) - the one the data got uploaded to, and it's the one I want to keep (3) - guest account.

I would like to delete (1) and (3), and keep (2) where all my data is.

The problem I am experiencing is when I log into (2) and press - symbol trying to delete (1) or (3), the minus is not active/ not responding. I am logged in and the lock symbol is unlocked.

Does anyone know what the problem might be and how I can solve it, please?