Z3 Roadster (E36/7) Engine Management Software Query

After purchasing my 2001 2.5i (83,300 miles), the garage updating my Z3's maintenance did a software update/upgrade with no detailed explanation except that I would appreciate the performance change.

How many versions of software are available?

What parameters would have been changed?

How would engine performance change with the newer iteration of software?

Anything else that would be noticeable? I'm getting a consistent 24 mpg overall, observed over 2,000 miles of city and highway driving.

If it was a factory update, you may or may not notice a performance difference. Updates are released for many different reasons - emissions control - shifting on auto transmissions - different driveability concerns - etc. Just like when your PC does an update on Windows. You may not see a difference in your screen or the operation of your computer, but they felt that something operating in the background needed to be changed.