This is a handy tool which is regularly updated by our friends over @Nomasis AG to calculate the upgrade path for on premise CORE and Sentry servers, I use this regularly and has been proven to be accurate, as always, check the product documentation and with your MobileIron Sales Engineer for exact upgrade tasks and path specific to your environment:
http://www.nomasis.ch/en/products/device-management/mobileiron/mobileiron-update-path.html