STM32 + LwIP where are the FS files and how to modify these ?

[Ciuffoly www.audiodesignguide]

I am able to compile and modify the LwIP example but where are the FS file and how to modify these and upload on STM32F746-DISCO ?

file  httpserver-netconn.c
 
 
     if ((buflen >=5) && (strncmp(buf, "GET /", 5) == 0))
      {
        /* Check if request to get ST.gif */ 
        if (strncmp((char const *)buf,"GET /STM32F7xx_files/ST.gif",27)==0) 
        {
          fs_open(&file, "/STM32F7xx_files/ST.gif");  <<<<<<<<<<<<<<<<<<<< ?
          netconn_write(conn, (const unsigned char*)(file.data), (size_t)file.len, NETCONN_NOCOPY);
          fs_close(&file);
        }   
     ..................
        else if(strncmp(buf, "GET /stat.html", 14) == 0)
        {
           DynWebPage(conn);
        }
        else if(strncmp(buf, "GET /SELECT_OPT", 15) == 0)
        {
        	LCD_LOG_State("Received a change to Optical ");
        	buttonOPTClicked();
        	sendOK(conn);
        }
        else if(strncmp(buf, "GET /SELECT_AES", 15) == 0)
        {
        	LCD_LOG_State("Received a change to AES-ABU ");
        	buttonAESClicked();
        	sendOK(conn);
        }