Change your Minecraft server version

Pick any game version in Settings. Players need a matching client version to join (Java players can pick one in the launcher's Installations).

Updating

Going up is safe: worlds upgrade in place the first time they load. latest follows new releases automatically a few days after they ship, once Paper supports them. Plugins and mods sometimes need their own update for a new version; check the catalog first.

Going back down

Going down usually isn't safe: newer blocks and items don't exist in older versions. On a paid plan we restore the backup taken before the upgrade instead. On the free plan, download the world before you update.