Hi,
I am not sure exactly what you need but if you need an easy to use client software and use Firefox as a browser, search for a free addon called, "FIREFTP". You can setup an account and save all settings for whatever ftp site you want to connect to, so with a couple of clicks, you should be able to connect. The UI gives whatever local storage on the left and the remote site on the right. Just highlight whatever file/ directory you want to move and click on the directional arrow in the middle.
If I am totally misunderstanding you, here is a link to setting up an FTP server on your NAS, not sure if that will help either but.....
https://www.youtube.com/watch?v=BCxdGWmrcOM&feature=related