Hi Grupodw, see this forum post:
forum.virtuemart.net/index.php?topic=102314.0
The solution has been provided there.
Deleting this additional price would require you do some changes in the Virtuemart Core files.
We don't provide any kind of Virtuemart Core changes in this forum, because it is not recommended. Eventually your change will retrieve back to stock once you perform the Virtuemart update.
Regards.
Forum Support.