...
Follow the steps in this article about how to Manually Setup the JRE.
Check Database Driver
Check that the version of Java and the Postgres JDBC version match up and and update accordingly (see setup instructions in this same article for details).
Key Files
Over time this may change, for example the user.sh file was added when moving between Confluece 3.x and 4.x. So, whoever does the upgrade please update the notes below,
...