Control Panel Location:
The ExpressionEngine Forums make use of “themes” to determine how they are displayed. The Forum Module comes with a “default” theme, which is located in your installation under themes/user/forum/.
In order to edit the Templates inside the Control Panel, set the theme folders and files to be writable. See File Permissions for details.
If you plan to make changes to your theme, we recommend that you make a copy of the themes/user/forum/default/ directory, name it something else, and make your changes to that one. You can easily switch themes simply by choosing a new one under Default Preferences.