Updating through the updater
If you downloaded the complete ZIP archive from the homepage, an updater program will have been included with HDoujin Downloader (“updater.exe”).
To update, open HDoujin Downloader and go to “Help > Check for Updates”. If updates are available, click the “Download new version” button and the update will be downloaded.
If you downloaded the standalone “executable-only” version of HDoujin Downloader, you won’t have the updater included and will need to update manually. This process also works if you’re unable to update through the updater for some reason.
All you need to do is go the homepage, and download the latest version from one of the download links there. Extract the ZIP archive you downloaded over your existing HDoujin Downloader, replacing all files (it might be a good idea to create a backup of this folder first just to be safe!).
This will overwrite your existing copy of HDoujin Downloader with the latest one, and you can continue using it normally. Your settings will carry over to the new version.