As your subscription has expired, you need to renew it so as the software could receive updates again . And post that if you wish to keep the firewall part alone, run the MCPR removal tool from Useful links and the top of the this page and login back to McAfee account page from here : http://us.mcafeee.com and do a custom installation selecting only firewall by which the other components would be excluded.
If you don't want to renew then you must uninstall it as it's basically useless without a subscription. The SecurityCenter can't be configured to use McAfee Firewall only and even if it was it's the whole suite that's on subscription so the reminders will continue.. There are free firewall applications out there. In the meanwhile if you are using XP SP3 or a later OS use Windows Firewall until you find a suitable substitute, it's better than nothing.
McAfee Removal Tool is linked under Useful Links at the top of this page by the way.