You should be able to go to your Registered account and de-activate. Then proceed to re-install from your account. Just in case here are the Guidelines/Instructions : How to uninstall or re-install supported McAfee products using the Consumer Products Removal tool
Edit: Moved to Consumer > General Discussion > Discussions
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Call (or use online chat) your local Customer Service department, they will free up the licence when you explain to them what happened.
Toronto ▪ Canada
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2 replies are better than none at all ;-)
And at the same identical time, to boot !