Google is usually a good place to start. Just type Adobe Lightroom, and the version you're looking for.
* go to adobe.com
* click on downloads - see all downloads
* click on product updates.
* search for Lightroom
Same links as Hal P Anderson provided, except now you'll know how to do it in the future if you've lost track of the links .
This link does not lead to where Adobe Lightroom 5.0 is available.
The highest level shown is Lightroom 3.6 Does anyone have link for Lightroom 5.0 version