Servers do not update automatically - whether this be the version of MineCraft when a new version is released, a new version of a modpack or a new build of Spigot etc..
How you update depends on the server version you are updating, and may require a quick log into the server files.
We always add separate options for the Vanilla updates to our list, and update the Default option when a new release is available.
To update you can either select the option for the new MineCraft release on the drop down list on MultiCraft and restart the server, or if you use the Default option you can log into the server files and delete the jar folder and restart to update.
These options are updated regularly for new patches/fixes and your server should also be kept up to date, but it is never automatic. To update when the same MineCraft version of Spigot/PaperSpigot has updated simply log into the server files, delete the jar folder and restart the server.
When the MineCraft version itself updates and Spigot/PaperSpigot release their updates for that release they will be added as new options on the list - simply select them and restart the server to update. Note that waiting a while for the first waves of bug fixes and patches and for plugins to update is always recommended, and plugins must always be kept up to date when using the newest version of Spigot/PaperSpigot as well.
This option is also updated regularly for new patches so this should also be updated regularly by logging into the server files, deleting the jar folder and restarting the server.
When a new Recommended version of the modpacks on our list come out they will be added to the list as a separate option - you just need to select it and restart the server to update.
For custom installations you will need to upload the new version of the modpack as you did for the version you are already using in order to update.
If your server is up and running with Forge and you are not changing the mods in any way then you do not need to update the Forge build even if a new build is available. This is particularly true if you use the plain Forge options on the 1-click install list as they will wipe the mods folder on the first install.
**Please note that a backup of your world is always recommended to be made before updating regardless of whether it is a Vanilla, Bukkit, Nukkit or Forge server - any update can cause issues and/or break worlds!