Well, PRTG is not that kind of monitoring tool. PRTG monitors network appliances and servers. AWStats is a dedicated website analysis tool, like Google Analytics or Piwik. There's no way to monitor these metrics within PRTG I'm afraid.
Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.