When you run ./manage.py syncdb, Django will look for any new models that have been defined, and add a database table to represent those new models. However, if you make a change to an existing model, ./manage.py syncdb will not make any changes to the database.
This is where Django Evolution fits in. Django Evolution is an extension to Django that allows you to track changes in your models over time, and to update the database to reflect those changes.
links for 2009-06-09