Change the Minecraft version or install a modpack

Your server runs one .jar file, and it decides the Minecraft version and whether the server takes plugins, mods or neither.

Which server type you want#

Change the version#

1. Stop the server from the Console tab, and take a backup.
2. On the Startup tab, change the version setting, often Minecraft Version, to the one you want, such as 1.21.1, or latest. Leave any Build Number on latest.
3. On Settings, press Reinstall Server. It downloads the new jar; your world, plugins and configs are normally kept.
4. Start the server and watch the Console until it says Done.

Pick the right Java#

If the console shows UnsupportedClassVersionError or class file version as it starts, the Java is too old. Choose a newer one from the Docker Image list on Startup, then restart.

Install a modpack#

With an installer, if your server has one

Some servers have a modpack installer, as its own tab or an option on Startup. If yours does, choose the pack or paste its CurseForge or Modrinth link, pick a version, and let it install. Back up first.

By hand

This works for any pack with a server pack: on CurseForge it's under the pack's Files; on Modrinth, look for a version marked as a server pack.

1. Download the server pack, stop the server, and take a backup.
2. For a clean start, delete the old world, mods, config and libraries folders in Files.
3. Upload the pack's .zip to the top folder, open its menu and choose Unarchive. If it unpacks into its own folder, move what's inside up a level.
4. Read the pack's README: it says which file starts the server and which Java it needs.
5. On Startup, set Server Jar File to that file, and pick that Java. If the pack starts from a script rather than a jar, open a ticket and we'll help.
6. Start the server and watch the Console. A big pack's first start takes several minutes.

When it won't start afterwards#