I am upgrading my current Splunk installation from 5.0.7 to 6.1.4, is there an easy way to back out the upgrade if something goes wrong? I do have a backup of all the configuration files already.
You should also back up your indexed data. See Back up indexed data in the Managing Indexers and Clusters of Indexers manual.
With your /etc directory and your indexed data backed up, it should be straightforward to reinstall the earlier release and then copy the backed-up information into it.