The page below has upgrade documentation:-
http://www.webwiz.net/webwizforums/kb/The active members page is always going to be a 'best effort' type of thing and never 100% accurate. The reason for this is that HTTP is a stateless protocol meaning that you only connect to the server while the page is downloading as soon as the page is downloaded you are disconnected.
Due to there not be a permanent connection to the web site you are viewing the server does not know if you are reading the webpage or have moved on to another website.
To get around these limitations web servers use sessions linked in to cookies and other ways to try and identify the user as being the same person as they move around the website. These sessions last 20 minutes after the last activity by the user.
This means that items such as active users will never be 100% accurate and are more of a guide to give you an idea of how many people are active on your website/forum.