I am admin on my photo gallery, but I get this message:
You don't have permission to access /update.php on this server.
If you are seeing an error message without a way to log in, then see the docs:
Authorization check (http://documentation.coppermine-gallery.net/en/upgrading.htm#updater_authorization)
Look for the bullet / section: "If everything else fails". Follow those instructions.
This seems to be an error message of your web server, not a message from Coppermine, right? Please attach a screen-shot.