Hi Luis - It depends on how many processes are assigned to each process(node). I do not think you you can manually assign RAM. If you have 20 gb RAM and still see that you can use remaining ram power, add few more processes to each node which can also improve your server performance.
But the less utilization of RAM may also been because there are less dashboards/extracts on server. But if not and there are already many dashboards/extracts on server, then Yes its worth adding extra processes.