What't the operative system of your servers?
Linux UFs are easy to upgrade using a remote script shell that you can find in Community (if not I can send you!).
For Windows UFs, you have to use a SW distribution tool.
I have to update a lot of Windows UF and try the new app in the splunk base (https://splunkbase.splunk.com/app/5003); this app distribute the installation itself from the Deployment Server to the UF and run the installation.
I did not get the installation to run, it seems the SplunkForwarder Service cannot perform an installation. If I run the scripts manually, it works.
Did you know if an installation via the SplunkForwarder Service is possible?
I would recommend using some kind of configuration management system to do this on scale. If you those are Linux (should work on Windows too) I think Ansible is a good solution for this task.