How to upgrade the software from v.7.8 to the latest one?
If the application has been installed in its default directory, then you can download the package from the Download page and overwrite your current installation. Or you can remove the previously installed version and install the latest one. I have checked the website, but there is no updated package available for this process. You can do it through a fresh install or over your current installation.
Download page: http://www.faststone.org/FSCapturerDownload.htm