The highest you can update your software to for free is Lightroom version 5.7.1.
The message you receive may have been about Lightroom 6, which is a paid upgrade.
If not, then please post the exact message you received along with some details about your system - thanks!
I'm trying to update 5.7.1, when I open Lightroom I get a message telling
me there is an update available. When I click to download, I get the
This file does not have a program associated with it for performing this
action. Please install a program, or if one is already installed, create an
association in the default
programs control panel.
I also downloaded 5.7.1 from the web-site, when I tried to install
it, I got a message saying I'm not eligible for this update.
What next? I know if I wanted version 6, I would need to purchase it.
On Sat, May 16, 2015 at 8:46 PM, ProDesignTools <firstname.lastname@example.org>
Are you sure you have Lightroom version 5 now? (Help menu > About Lightroom)
If so, then you would be entitled to update to Lightroom 5.7.1 at no charge, since it's the same major release.
You should be able to download it from the updates page: