Before activating the license key, you need to have the PRO version of the purchased theme/plugin installed and activated. If you need help installing a theme go to the “General Settings” section.
For themes: To activate the license key go to your WordPress Dashboard under “Appearance-> Theme License” and paste your license key in the box.
For plugins: To activate the license key go in the plugin options page, scroll down the page until you find the section called “License Key”, paste your license key and click on the “Save Changes” button. Then, after the page is saved, you can click on the “Activate License” button (you will see a gree check mark next to the license key).