Depends in what application you try to access that information. If your just looking at the file in windows right click and go down to properties and you should be able to see the file size that says "size on disk" that is the one your most concerned with that's the one that must be under 40k which in the picture I posted was extremely low. The original of it was 600k.
If you have an application for editing pictures sometimes they will have a button or drop down that says "Image information" click on it and it should have all necessary info.
There are three different ways of getting your file under the 40k size requirement that I can think of. Number one thing you should do is crop out any area of the pic that is not necessary, secondly resize the picture and thirdly if your still not under the file requirement when you save the picture you often times can change the quality of the image.
Hope this helps
OSO really should have a better help file on this!