_upgrade_preupgradechecks
Check the Upgrade Notes for the version you plan to upgrade to (and any in between).
Go to Administration > General Configuration > Plan your upgrade then select the version you want to upgrade to. This will run some pre-upgrade checks.
Go to Administration > General Configuration > Troubleshooting and support tools to run the health check.
Go to Administration > Manage apps and scroll down to the Confluence Update Check to check the compatibility of your Marketplace apps.
Choose the version you plan to upgrade to then hit Check.