Dataset Upload issue

I have created an upload button so as users can upload pictures to my website.
I have created a dataset with the PK field Title and another field Photo to hold the photo.
I have put this code behind the button:

This code works fine but when I go to the database it has created a new field [Photo] along side the original field. And is saves two copies in the media file as well. is there code that just inserts into the existing field instead of stFieldValue.