Under “Downloads”, you will see your downloadable files.
Download the plugin file. It should look like essential-addons-elementor-pro-2.x.x.zip
Go to your Plugins page from WordPress Dashboard.
Click on “Add New” and upload the plugin file and activate.
After activating the plugin, you should be redirected to the plugin options page where you can configure the elements. Enable/Disable the elements and hit save button.
Note : If you already built something with the free version, you won’t lose them. After activating Pro, those will appear same as before. You can still save the pages as Elementor templates. It’s always good to have backups.