nGen file field: how edit and deleting in SAEF?

I have installed the nGen file field and inserted in my SAEF. Uploading a new file works well, but how delete the file and upload a new file?

This is my code:

{if field_id_12}
   /images/uploads/register/{field_id_12}
{/if}
   <input type="file" name="field_id_12">
   <input type="hidden" name="field_id_12[file_name]" />
   <input type="hidden" name="field_id_12[existing]" value="{field_id_12}"  />

The code works well when there isn’t a file yet. But if there is already a file and i want to upload a new file, the old file keep existing.

So, anybody have a good solution for nGen file field VS a edit SAEF