- On the left hand side of your control panel click "Config Files".Choose the first file named "Server Settings"
- Scroll down to the level-type field.
- There are 4 types of world to choose from DEFAULT, AMPLIFIED, FLAT or LARGEBIOME
- Choose a world type and enter it into the box and click "Save"
- Delete your current world or create a new one. (See here)
- Start your Minecraft server.
Please see here for an explaination of each world type.