A seed only controls how a new world generates, it does nothing to a world that already exists on disk. To actually get a new seed, the old world has to be deleted first.
How to reset your world
- Open Backups and take a snapshot first. This is your way back if anything goes wrong.
- Click Stop to shut the server down.
- Open Server Properties and set the seed field, or leave it blank for random.
- Open Files and delete the world folder, and its nether/end companions if present.
- Click Start. The server generates a fresh world using your seed.
Only delete a folder you're 100% sure is the active world. If it's named oddly, like
world1orworld_old, treat it as a possible backup and leave it alone until you've confirmed otherwise, deleting the wrong folder is the most common way players lose builds permanently.
Still stuck?
Server won't start after deleting the world: check Console for the crash reason, often an incompatible world-generation mod. See How to Read the Crash Log.
Switching modpacks entirely, not just the seed: use How to Install a Modpack instead, it handles the world swap for you.
Deleted the wrong folder with no backup: open a support ticket, our team can check the panel directly.
Did this solve it?
If you are still stuck, our team can look at your server directly.