The User Configuration Data Exists screen presents options for removing the configuration database:
If you want to maintain the configuration data in the database, for example when you plan to upgrade or migrate to another database, make sure that these options are not selected.
Uninstalling WS_FTP Server 2017 leaves behind registry entries for PostgreSQL. This prevents installing older versions of WS_FTP Server such as in a rollback situation. The Registry values are:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\PostgreSQL Global Development Group
Reinstallation of the older version installs the appropriate ODBC and jumps past the install of PostgreSQL and the creation of the local user service account and asks for the PostgreSQL connection information. If you enter the information for port, user, and password it will fail to connect.