To uninstall G6 FTP Server, remove it via the 'Add/Remove Programs' item of the Control Panel or use the shortcut in your start menu.
After uninstallation, delete the configurations files (Accounts.ini, Groups.ini and Ftpsrv.ini).

The only remaining exe is the "_g6uninst.exe" (~20Ko) in your windows directory, you can delete it after uninstallation.
That's all.