title: Update FileField filename after uploaded file saved (Django)
body: <p>How do you change the filename of a media file (user-uploaded file) in Django <strong>after</strong> it's been saved?</p>
  
  <p>I understand that if you want to do it <em>as it's being uploaded</em> that you can follow the solution in questions like <a href="https://stackoverflow.com/q/2546575/2588818">this</a>, but I'm talking about changing the names of images that are already in the database.</p>
  
  <p>I have tried overriding the name attribute of the <code>ImageFileField</code> and then saving the model, but this does not affect the file itself. It just breaks the reference because now the <code>ImageFileField</code> is pointing at the new name but the file still has the old one.</p>
  
  <p>Using the same example model as the linked question:</p>
  
  <pre><code>class SomeModel(models.Model):
      title = models.CharField(max_length=100)
      video = models.FileField(upload_to='video')
  </code></pre>
  
  <p>This does NOT work:</p>
  
  <pre><code>&gt;&gt;&gt; for m in SomeModel.objects.all():
  ...   m.video.name = 'new_video_name.avi'
  ...   m.save()
  </code></pre>
  
  <p>What <em>should</em> I be doing here?</p>