Resetting your server is an important feature if you're looking to wipe your server clean. This will delete everything on your server. Worlds, plugins, and any other data you've created on your server. Your server name is not affected.
Server Dashboard / Edit Server / Danger Zone
Once there, you'll see the Reset Server button. Once you do this, it cannot be undone. Make sure you're okay with your choice. To reset your server, click the button, and restart.