When an upgrade is attempted, you do get an option to backup your existing versions database. That database can only be restored as long as the server's unity version is the same. When Unity is upgraded, it keeps the database intact and upgrades the software version as well as database structure etc... If any thing wrong happens with the upgrade, you have to install the same old version of Unity (3.14 in your case) and then do a restore of the database from the DIRT backup and re-do the upgrade.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...