Hi,
The classical upload custom field do not have a "delete" feature ; but the "ajax file" one have.
You can see to modify directly the data in the hidden input field (using the browser inspector).
You can see to change temporally the custom field into a "text" so you can edit and empty the field.
You can see to switch, at term, to the ajax file file.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.