Each time we release a new version, emails with download link are sent to all users who purchased Sitecake. Simple way to do an update is just to replace sitecake/ folder with the new one. This will work, but it will replace all configuration files with default configuration, including resetting your password to 'admin'.
Smarter way to do the update is to upload folder that holds new version next to the folder with old version and keep configuration files intact. You can rename sitecake.php to sitecake-231.php or something similar and place new sitecake.php in the root.
├── 2.3.1/ (old version)
├── 2.3.2/ (new version)
sitecake231.php (old version)
sitecake.php (new version)
Now you can test how the update works. In case you want to roll back, just rename back sitecake231.php to sitecake.phpand you are back.
We plan to introduce silent update process. This will make your Sitecake update the same way modern browsers do. You don't even notice when it happened.