Once there is a new version, you'll be prompted by the window below:
Click Update Now to update DVDFab.
Or, you can check for updates in the Settings menu on the top right corner of the DVDFab main interface. When there is a new version, you'll be prompted with the first window as mentioned above.
You can always go to the download page https://www.dvdfab.cn/download.htm to download the latest version and then install it to get updated manually.