How can I delete existing downloads on the product?

Example of a JSON call for the Sync API (UUID of the download entry must be known): POST http://www.my-shop.com/api/_action/sync

[
    {
        "action": "delete",
        "payload": [
            {
                "id": "0189f2466f197d7b808601c970f8d034"
            }
        ],
        "entity": "acris_product_download"
    }
]

Attention: The medium itself is not deleted with this call. It must be deleted via an additional call with the known UUID of the medium: DELETE http://www.mein-shop.de/api/media/0189f2466ded7927a13d3904b7d1a0a2