Run cmd.exe (regularly, no need to run as Administrator), and enter the following:
cd "C:\Program Files\Softgenetics\Softgenetics Server\pgsql\bin"
set PGPASSWORD=softgeneticssetup
pg_dump -U postgres -d softgenetics -f [backup_filename]
Note: replace [backup_filename] with the actual path and filename, e.g.
pg_dump -U postgres -d softgenetics -f C:\Users\Public\Documents\softgenetics_backup.sql