In your back office, either up at the top for very old versions or down on the bottom for newer versions.

I don't know a user or pass. I just installed it for someone else and I can't get a hold of them. I have shell access and I was hopiing it maybe in a file or the DB somewhere.

It's in conf/_application.php as the value for $app_version. The database contains a schema value that can sooner or later be translated into the human-friendly version, but it's much easier to get the human-friendly straight off eh?