Where do I enter my license key?

I have the free Internet Security trial right now, but I purchased a license key from a third party.  I cannot find where to enter the key anywhere.  I found a page that said it was under Options, but there is no place to enter it there.  Is this because my trial is still going?  Where can I enter it?

Hello Chris,
Please be informed that you might have installed the AVG Internet Security with the Zen Interface. Please follow the instructions on the article http://support.avg.com/SupportArticleView?urlname=How-to-reinstall-AVG to reinstall all the traces of the AVG program and check whether it resolves the issue.
Note : Please use the AVG Remover tool mentioned on the article to uninstall the AVG program more effectively.
If you are still facing any error message please provide us with the screenshot so that we could analyze the issue more better. Please follow the instructions on the article http://avgclick.me/getscreenshot to create the screenshot.
Please feel free to get back to us for further assistance.
Thank you.