In the Establishing Server Staging Environment the documentation notes the following:
Tip: JIRA has a tool to manage any changes in your installation. Check the System Information page in the UI for "modified files." This will tell you which files have been customised in your installation directory.
I am running 5.1.1 and when I go to the System Info page under Admin Troubleshooting and Support and need clarification on which specific files I need to review.