So you have been optimistic enough to upgrade Magento to the latest stable version using connect.

Three ways to solve the 500 server error message and get your site working again.

1. Set permission 755 for magento folder and index.php
   - If the site does not display after you have checked the file permissions, get in touch with your host. More on this here.
2. Sometimes the files are set to 600 on shared servers and only your hosting provider can change this. It pays to have a good host with live chat or telephone support.
3. Check the .htaccess file – this is overwritten during the upgrade process – especially if your install is in the /root, rather than the /magento standard location – check “RewriteBase /” or “RewriteBase /magento”