Server software and version are set in your startup configuration and can be changed without rebuilding the server from scratch.
- Back up first. Version changes touch world data.
- Check that your plugins or mods support the target version before switching.
- Stop the server, change the version or software in the startup settings, and save.
- Start the server and read the console through the whole startup.
- Join and check a few known locations before announcing the update.
Downgrading
Rolling back to an older version after a world has been opened on a newer one is often not clean, because world formats change. If you need to downgrade, restore the pre-update backup rather than changing the version back.