How to change PostNuke Themes (Templates)
In order to change your Postnuke Theme, please, follow the step-by-step instructions below:
Themes for Postnuke can be found at http://themes.postnuke.com
Download the theme and unpack it on your PC.
Upload the extracted folder to the “Themes” folder on your site.
Login as Administrator.
Then go to the Administration Panel and click "Settings".

Go to the Themes area and click on the drop-down menu.

Select the Theme you installed from the drop-down menu as "Default theme for your site"
Scroll down to the bottom of the page and click "Save Changes".
The theme will become active immediately.