[Zope] manage_edit or manage_upload help

Hi, I have created a file object from the OFSP product using manage_addFile. This works great. Now I am creating a form to edit the contents of the file. On submitting this form, I want the file data to be updated with what was there in the textarea of the form. Seems simple, and I tried to use manage_edit or manage_upload from my python script. I am unsuccessful in doing this and get Attribute Errors. I would appreciate it if someone could send some example code to help me update the contents of a file object. Thanks Ravneet