Form alter hook in Drupal 6 I have created a content type in which I have a field that is a select box.
Now I want to change all the default values of that select box.

I know hook_form_alter() will work this, but I have no idea on how to change this.
Is anybody able to give me an idea?
Just adjust the values of the form element to your needs. Check this http://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/6#select to see how selects ar build using FAPI.