something like this:
import os.path
from app.models import Model
prefix = #new folder location
ms = Model.objects.all()
for m in ms:
oldname = m.fileField.?? #get old path name
basename = os.path.basename(oldname) # Get the filename by itself
newpath = os.path.join(prefix, basename)
#store it back on the object
m.save()