If you have a previous version installed and want to upgrade, then please follow these instructions:

1. Make a backup of all your data before you do anything else!
2. log in to your existing site, and under the admin panel (settings) unselect the 'site enabled'. Note the current version of your site.
3. upload all the new files *except the settings.php and skin files* to your server, overwriting the old files.
4. visit the /install/upgrade.php file using your web browser, and choose upgrade

If you have a large number of articles, this can take several minutes as the upgrade creates new indexes on the articles.

When done, you still have to upgrade the skins. In the admin panel, select 'Manage skins' and choose 'upgrade' next to your skin name. (this will add the 'members' template)