Change the default port in the service
To change the default port on the service, you need to change the execute command string.
In Windows, you can do this by changing the Registry Entry at:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\services\fcdocservice
CODE
"-Djava.library.path="C:\xampp\LibreOfficePortable\App\LibreOffice64\program" -jar FCDocConverter.jar 9080"
It will look like this:

Restart the Windows service from the FileCloud control panel to make this change effective.
Change the port that FileCloud uses for Docconverter
Open the FileCloud config file (cloudconfig.php) typically located at C:\xampp\htdocs\config
Go to the end of the file, and add the following entry (in case the parameter already exists, only change the port number):
CODE
define("TONIDOCLOUD_FCDOCCONVERTER_URL", "http://127.0.0.1:9080");
Now, all preview requests will go to the new URL/port.
Changing the IP address for Docconverter
In case 127.0.0.1 can't be used, you can change this in the registry and the config file.
The IP address can be added at the end:
CODE
java -Djava.library.path="D:\xampp\LibreOfficePortable\App\LibreOffice64\program" -jar FCDocConverter.jar 8080 192.168.1.108
You can make this change and restart the service.
Then, you can change the config file to have this URL/IP address used:
CODE
define("TONIDOCLOUD_FCDOCCONVERTER_URL", "http://192.168.1.108:9080");