Deleting attached pdf file

i would need the same, because i am exporting every week 10 pdfs into an imagefield to get it printed afterwards. but i just need it one week. later i dont need it anymore.
so i also would need to have a code to get the context of some image-field deleted.
This will reduce the Database-Size when i want to export it. if it wouldnt delete the PDFs inside, i would have a 10x size of the database.

Some code which makes this step on the image automatically, would be phantastic!

i found a way to delete a file which is in a image-field:

'image field' := null

if you need to delete several fields, this works:

'image field1' := null
+
'image field2' := null
+
'image field3' := null
+
'image field4' := null