When you open your KB, it displays all the categories with 5 articles underneath, I've been in conversation with DeskPRO who advised... By default, the top 5 are the most recently added Articles. We don't have an option to customize this in the UI. It may be possible to alter by editing the portal templates. Alternatively, you could raise this in our feature request/feedback area.
I should be able to choose what top 5 articles should be listed or within the site, instead of it displaying the top 5 most recently added, how about showing the top 5 most used/viewed articles ???