Here you'll find a list of files and downloads for OPnPW. If you're a new user you'll want to just download the main installer. If you're an existing user, there may be an update out for your version of OPnPW.
     Currently, to check your version within the program press "Help" then select "About". This will then show your version at the bottom.

OPnPW Full Install Version 2.0.9
OPnPW Update For Version 2.0.6 and later.