The Versions tab changes which Minecraft version and which server software your service runs. It is the convenient way to do something that is genuinely risky, and the convenience is exactly why the backup step gets skipped.
A version change rewrites server files and, on first start, upgrades your world to the new format. That upgrade cannot be reversed — an older version will refuse to open the world afterwards. A backup taken and downloaded first is the only route back.
What to do
- Check your plugins support the target version
Do this before changing anything. A server that starts on the new version with half its plugins disabled is worse than one still on the old version.
- Take the backup and download it
On your own machine, and open the archive to confirm the world folder is inside.
- Select the version and apply
The panel fetches the new server software. Watch the console output — it tells you what it actually installed.
- Start and read the startup banner
It prints the version. If it does not match what you selected, stop and check the jar filename in Startup before letting it load the world.
- Update your plugins in the same session
Doing both at once means one round of testing. Doing them a week apart means you cannot tell which change caused a problem.
What each kind of change costs
| Change | Risk |
|---|---|
| A minor version — 1.21.1 to 1.21.3 | Low. Most plugins carry over. |
| A major version — 1.20 to 1.21 | Moderate. Expect to update plugins. |
| Paper to Purpur, or similar | Low. They are compatible forks. |
| Paper to Fabric or Forge | High. Plugins do not work on mod loaders at all. |
| Going backwards a version | Very high. The world may not open. |
A splitter slot gives you somewhere to restore a copy of the world and try the new version before it becomes the real one. That converts an anxious evening into a routine change.
The console reports the version you chose, every plugin loads without an unsupported-version warning, and you can walk around your world normally.