FolderSizes has a built-in update checking feature, accessible from the Help section of the application ribbon bar.
Behavior of update checking can be configured through the options window.
The update checker window indicates the current installed version of FolderSizes, as well as the version of the latest publicly available product build. If the latest public version is newer than the installed version, you may elect to upgrade. Clicking the Download button will take you to the download section of the FolderSizes product website. Click the Info button to learn more about what's new in the latest release.