(In 1024 simple steps)
Include as few upgrades as possible in your upgrade process. For example, instead of upgrading from GitHub Enterprise 3.3 to 3.4 to 3.5, you could upgrade from GitHub Enterprise 3.3 to 3.5. Use the Upgrade assistant to find the upgrade path from your current release version.
HOWEVER the next paragraph:
You must upgrade from a feature release that's at most two releases behind. For example, to upgrade to GitHub Enterprise 3.5, you must be on GitHub Enterprise 3.4 or 3.3.