Method 1:
- Login to your control panel.
- Enter your configuration editor, click text editor next to serverconfig.txt
- Find the 'difficulty' line and change the value to the number for what difficulty you want. Numbers are 0 for normal, 1 for expert, 2 for master and 3 for journey.
- Save and apply.
- Restart your server.
Method 2:
- Login to your control panel.
- Enter your configuration editor, click configuration editor next to serverconfig.txt
- Ensure the auto create check box is checked
- Change the difficulty dropdown to the setting you want.
- Save and apply.
- Restart your server.
Note: You will need to generate a new world for this to work, for help on how to generate one click here.