Check that :
- Apache can physically access the file (the user that run apache, probably www-data or apache, can access the file in the filesystem)
- Apache can list the content of the folder (read permission)
- Apache has a “Allow” directive for that folder. There should be one for /var/www/, you can check default vhost for example.
Additionally, you can look at the error.log file (usually located at
/var/log/apache2/error.log) which will describe why you get the 403 error exactly.
Finally, you may want to restart apache, just to be sure all that configuration is applied.
This can be generally done with
/etc/init.d/apache2 restart. On some system, the script will be called httpd. Just figure out.