Hello danp,

you can update TemplateSwitcher just as any other extension.

First, download the latest version by logging in to on our site, you can find the download link in your account/your orders.
In the backend of your site, go in the menu to Extensions -> Manage ->Install, and upload the ZIP file.
In the case of the TemplateSwitcher, you must unzip the original ZIP file first, as the TemplateSwitcher consists of a module an a Plugin.
Upload/Install the module zip file and the plugin zip file separately.
Finally, make sure that the plugin is activated and the module configured correctly.