About software upgrades in general and Tiki.
It depends of how far you’ve been in customising on your side and what was changed from version to version.
Your Tiki14.x is a pre LTS and you should already jump to version 15 for safety.
It seems that shouldn’t be a big jump : https://doc.tiki.org/tiki15. Check your PHP version. ;)
With that you’ll be on the safe side till 2021.
A jump to Tiki18 is a bigger one but with many many improvements and advantages. To review them you have to check:
and of course https://doc.tiki.org/tiki18
In my mind once you’ve done the Tiki15 and everything is ok and fresh in your mind (like the list of customised files) you should go for Tiki18... So many fixes, so many improvements...
You can get available version from here: https://tiki.org/Download
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