To update one of your models using South, you'll first want to create a new schema migration by using the
schemamigration command and the
$ ./manage.py schemamigration some_schema --auto
if the model or fields were updated since your last migration, you should see something like this
+ Added model some_schema.ArticleCategory + Added field category on some_schema.Article Created
Next, when you're ready to apply the update you can run
$ ./manage.py migrate some_schema
Check out the official South tutorial for more details.