You need to activate Neutron's internal FTP server and attach it to one of the existing source entries: settings → Network → FTP → select source entry which will be managed by the FTP server. You will notice that IP address, generated username and password will be updated.
On another device use any FTP client (for example FileZilla) → enter IP, username and password → manage files via FTP client.
Neutron will auto-refresh source entry if file system is modified via FTP and when the Refresh button is switched on.
Note: Make sure that Network functionality is enabled in Neutron: settings → User Interface → Optional Features → Network = On.