This thread is resolved. Here is a description of the problem and solution.
Problem: The client would like to uninstall WPML, then reinstall it. He dies not want any language information set up on the reinstall. Further, he wants that all the translated images are deleted.
Solution: You can reset WPML but it will not delete translated media, translated posts and translated taxonomies.
Before proceeding please make a backup of your site and database.
Please go to Media and delete the duplicated media manually by changing the admin language in the top bar. Change the view to list and mark the checkbox for all items. Then select delete permanently from the dropdown.
Now go to posts. Here you will have to delete the foreign language posts manually. Do the same for the taxonomies (categories and tags).
For a fresh install of WPML please go to WPML -> Support -> Troubleshooting and choose the reset WPML option at the bottom of the page.
Relevant Documentation: https://wpml.org/faq/how-wpml-reset-works/
This is the technical support forum for WPML - the multilingual WordPress plugin.