Clear the Theme registry

For most theme developers, the registry does not have to be dealt with directly. Just remember to clear it when adding or removing theme functions and templates. Editing existing functions and templates does not require a registry rebuild.

To clear the theme registry, do one of the following things:

1. Clear button located at "Administer > Site configuration > Performance".
2. With devel block enabled (comes with devel module), click the "Empty cache" link.
3. The API function drupal_rebuild_theme_registry.

 

Excerpted from http://drupal.org/node/173880