Sometimes it's best to uninstall McAfee while upgrading a system then reinstall. If your online account is showing that you have an available license then try the following first:
Uninstall all McAfee via Control Panel > Programs and Features
Run the MCPR Cleanup Tool and reboot.
Download and install your software from the online account.
If there is a discrepancy in your license count on your online account page, then give Customer Relations a phone call, it's free of charge and available via the link under "Useful Links" at the top of this page. They can make adjustments to your account for you.