Minecraft - Changing or Wiping your World/Seed/Save
Log in to your Multicraft control panel. Link to Multicraft Login Panel
First click Files. And then click Config Files.

Click Server Settings.

To change the world and seed, scroll through the settings available and find Level Seed and Level Type.

If you have changed the world/seed while having a current save, you will need to change the save name.
The save name for your world is located in the following steps.
Click Show Advance Settings
Change the World to a different name in the field. This is your World's save name.

The following steps is only if you are looking at wiping your world/seed/save from a previous one.
Click Files and then click Config Files. See image above on Step 2.
Click Setup.

Check the box for "Delete All Server Files" and click Apply.

Start the server and click Console to watch for the server to complete the process.
First click Files. And then click Config Files.

Click Server Settings.

To change the world and seed, scroll through the settings available and find Level Seed and Level Type.

If you have changed the world/seed while having a current save, you will need to change the save name.
The save name for your world is located in the following steps.
Click Show Advance Settings
Change the World to a different name in the field. This is your World's save name.

The following steps is only if you are looking at wiping your world/seed/save from a previous one.
Click Files and then click Config Files. See image above on Step 2.
Click Setup.

Check the box for "Delete All Server Files" and click Apply.

Start the server and click Console to watch for the server to complete the process.
Updated on: 25/01/2021
Thank you!