Whenever Vanilla 1.14 is also released - Spigot generally releases their next release builds the same week as the Vanilla release.
In general however - when using a CraftBukkit/Spigot server you should not update straight away when it comes out. The early builds released will have bugs that need ironing out and plugins may not work on the updated version until they too have updated.
Running a localhost on Spigot 1.14 as it's released will allow you to test for plugin issues with the plugins you have but your active server should not be updated until you're sure you are ready to update and the plugins you use are also updated if needed, otherwise you may lose the use of some plugins and once it's updated it should not be backdated to 1.13 (unless you create a backup of the world on 1.13 first so you can restore it when you go back to 1.13, as a world loaded on 1.14 will not work well on 1.13 and may have any number of issues).
When 1.14 is released and you have updated the server jar will also need to be reinstalled regularly to keep up with patches/bug fixes - this is done by simply deleting the jar folder in the server files and restarting the server.