Can I safely update/upgrade SIlverSHielD to the latest version or will I lose my users and configuration?
The SilverSHielD installer (both Free and Pro version) will not overwrite your current configuration and user database, thus it's always safe to update/upgrade to the latest version.
At the same time, best practices suggest to backup any software configuration before performing an update/upgrade. SilverSHielD stores its configuration under a system-defined folder known as %COMMONAPPDATA%.
Such folder has changed its default location in the latest versions of the Windows operating system, so:
In Windows XP and 2003 it's usually
C:\Documents and Settings\All Users\Application Data
In Windows Vista, 2008 and 7 it's usually
The SilverSHielD configuration, server key, logs and user database are located inside a "SilverSHielD" folder under the above mentioned system folder.