How to switch to root user for command execution using Jsch in java?

I am trying to execute a set of commands over an ssh connection established using a private key. For this I used, JSCh and Session class in java.

Here is the code:

java.util.Properties config = new java.util.Properties();

         String privateKeyPath = conn.getsshArg().getKeyPath();

        config.put("StrictHostKeyChecking", "no");
        JSch jsch = new JSch();

        jsch.addIdentity(privateKeyPath); //

        Session session = jsch.getSession(conn.getsshArg().getUsername(), conn.getVmIpaddress(), 22);
        session.setConfig("PreferredAuthentications", "publickey,keyboard-interactive,password"); //

        System.out.println("User:" + conn.getsshArg().getUsername() + "Password" + conn.getsshArg().getPassword()
                + "IP:" + conn.getVmIpaddress() + " Port:" + 22);
        session.setPassword(conn.getsshArg().getPassword());
        System.out.println("Command to be fired:" + conn.getsshArg().getCommand());
        session.setConfig(config);
        //session.setTimeout(150);
        session.connect();
        if (session.isConnected()) {
            // LogManager.getLogger().info("VNFLCM: Ssh on the VNF
            // successfull");
            System.out.println("SSH successful");

        } else {
            System.out.println("SSH Connection Failure ");
            return ret;
        }

        Channel channel = session.openChannel("exec");
        String command = conn.getsshArg().getCommand().replace("&curlStart;", "{");
        command = command.replaceAll("&curlEnd;", "}");
        command = command.replaceAll("&jsonQuot;", "\"");
        ((ChannelExec) channel).setCommand(command);
        //channel.setInputStream(null);
        ((ChannelExec) channel).setErrStream(System.err);

        InputStream in = channel.getInputStream();
        channel.connect();

        byte[] tmp = new byte[1024];
        String line = "";

        while(true){
            while(in.available()>0){
                int i=in.read(tmp, 0, 1024);
                if(i<0)break;
                //LogManager.getLogger().debug(new String(tmp, 0, i));
                line=new String(tmp, 0, i);
                System.out.print(line);

            }
            if(channel.isClosed()){
                //LogManager.getLogger().debug("exit-status: "+channel.getExitStatus());
                System.out.println("exit-status: "+channel.getExitStatus());
                break;
            }
            ret = true;
            try{Thread.sleep(5000);}catch(Exception ee){}
        }

        channel.disconnect();
        session.disconnect();
    }

    catch (Exception e) {
        e.printStackTrace();
    }

I tried logging in using root user over my node, but a prompt for ssh using fedora instead of root was made.

I tried the solution provided in the link : Java JSch changing user on remote machine and execute command , but using su -c "command" prompts for a password. And here I don't have any password for my instance.

All the commands need to be executed using root user only.

Please note: Here, I am trying to ssh using a private key.

I would be grateful if anyone could help me in this.