There are no files to download and update, everything required for extended functionality already exists in the main application. If plug-in is not registered, it works in DEMO mode - you can do everything, but you will not be able to import more than 10 items at once. In order to unlock its functionality, you have to purchase appropriate license and register this extension.
Registration requires a license key. See these articles regarding registration issues. You can reset addon's license (due to hardware change etc.) in the same way as the main a software license (for Magento, PrestaShop, or WooCommerce).
Addon registration steps:
1. After the purchase all customers receive the email notification with registration information, you may find License Number (Regcode) there.
2. Open "Preferences" (F12) and activate the "Addons" tab. eBay Integration addon is listed there among other available addons.
Possible registration statuses:
"Unregistered" - extension works in DEMO mode
"Registered" - addon is registered and fully functional
"Verifying..." - software is checking registration information
3. Click on registration status, the "eBay Integration Addon" registration window will appear. Enter License Key and click the [OK] button:
Store Manager will check License code and return Addon status.
If activation is successful, you will see green color text "Registered".
Now eBay Integration Addon is registered and you're welcome to use it.