Erase all personal settings from mac I want to leave the software on my mac and the profile and all that but I want to erase all passwords and history and personal settings from the mac so that a new colleague can use it?
The safest way to do that is to encrypt your account with File Vault and then create a new account for the new user. Then it doesn't matter if he has admin access he can't ever access your files without your password.

Even erasing the account doesn't really get rid of the files. They could be recovered with a file recovery program. File Vault is the easiest way to keep things private.