In Django, if you delete a model that has Filefield or Imagefield, the related files aren't deleted from the filesystem. You can fix that in two steps:

  1. Add filecleanup function, that'll take care of deleting files attached to a model:

    import os
from django.core.files.storage import default_storage
from django.db.models import FileField


def file_cleanup(sender, **kwargs):
    """
    File cleanup callback used to emulate the old delete
    behavior using signals. Initially django deleted linked
    files when an object containing a File/ImageField was deleted.

    Usage:
    >>> from django.db.models.signals import post_delete
    >>> post_delete.connect(file_cleanup, sender=MyModel, dispatch_uid="mymodel.file_cleanup")
    """
    for fieldname in sender._meta.get_all_field_names():
        try:
            field = sender._meta.get_field(fieldname)
        except:
            field = None

        if field and isinstance(field, FileField):
            inst = kwargs["instance"]
            f = getattr(inst, fieldname)
            m = inst.__class__._default_manager
            if (
                hasattr(f, "path")
                and os.path.exists(f.path)
                and not m.filter(
                    **{"%s__exact" % fieldname: getattr(inst, fieldname)}
                ).exclude(pk=inst._get_pk_val())
            ):
                try:
                    default_storage.delete(f.path)
                except:
                    pass

  2. In models.py, add post_delete signal to catch model deletion event:

    models.py 
    from django.db import models
from django.db.models.signals import post_delete
from .utils import file_cleanup

# ... models code goes here ...

post_delete.connect(
    file_cleanup, sender=Image, dispatch_uid="gallery.image.file_cleanup"
)

And that's all. As you see in the example above, my sender is Image model, and when it's get deleted, it'll fire file_cleanup function that will take care of cleaning up files.