Benchmarking GitHub Enterprise
githubengineering.com
githubengineering.com
Prior to Enterprise2 upgrades are done with a package that updates the appliance 'in-place' and restarts services (or a reboot? It's been a long time).
Enterprise2 writes a new root file system on upgrade and starts from there. Files for this are distributed from either to enterprise homepage or the releases page, https://enterprise.github.com/releases/. In either page you'll find a link to a download page where a selection can be made for installation or upgrade.