I am trying to: I've changed some categories for the product in the default language. But now, there are not synchronize with the English version. How Can I synchronize my products after changes (categories linked to the product).
In case some posts got unsynchronized taxonomies, you can manually sync them by going to WPML -> Support -> Troubleshooting (it's a link), and using the "Synchronize posts taxonomies" button.
There you can select the post type, and after clicking the button the category from the default language will be copied to the translations (where the taxonomy is translated).
Please make sure to have a working backup of your site before proceeding.