UPGRADE from (too) OLD ver 1.8.20.1 to ver 14. How is that possible?

FreePBX Installation / Upgrade
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You have two viable options:

  1. Use this conversion tool to migrate your settings from your old system to a new 14 install: https://wiki.freepbx.org/display/PPS/Elastix+and+PBXinaFlash+to+FreePBX+Distro+Conversion+Tool
    Which will get you most of the way there, but some manual clean up is necessary, see this thread: How to: Upgrade FreePBX13 to FreePBX14 on Hyper V - Guide

  2. Do a backup of your old system, and restore it directly on a new 15 install. FreePBX 15 is the first version that permits restore directly from legacy backup tarballs.