I'm 99% percent 10.3.1 is a free upgrade for people who have 10.3. The idea is those kinds of updgrades are bug fixes with no real new features.

You should see 10.3.1 in your Wolfram User Portal. If not, then your university or site license should be able to hook you up with 10.3.1.

If for some reason you can't, contact wolfram customer service:

http://www.wolfram.com/support/contact/?source=nav

Changes since 10.3.0? Minor releases typically have bug fixes which are not documented. What specific changes are you interested in? If just changes between 10.3.0 and 10.3.1 you can simply run the same code in each and see fi there is a difference affecting a particular bug you may have interest in.

In the Documentation Center there is a link on a function's page at the top right hand corner that says "Updated: Show Changes" which you can click on to highlight changes since the previous major release. Also at the bottom left hand corner of the page is further history information. So, yes, I am puzzled about any changes in ActionMenu for example: I don't know of any and none are listed on the page--last significant change seems to be in Version 8. DynamicModule was updated in version 10 by adding the (very much needed) SaveDefintions option along with other things.

I am guessing that the final bullet in the list at the link you posted has to do with bug fixes--I agree that it is oddly worded to suggest that there are significant changes in design functionality aside from fixing internal bugs.

All fo the other bullets on that page are worded to indicate that they are bug fixes and modifications to already deployed functionality.

Perhaps a WRI employee can comment.