Note: In order to use the new seed, you will need to remove the old world folder as it must be regenerated. We have an article that explains the process here:

http://hosthavoc.com/billing/knowledgebase.php?action=displayarticle&id=36

The steps to change the level seed are as follows:

Step 1: Log into our Multicraft control panel.

Step 2: Open your service in the panel.

Step 3: Click 'Files' on the left -> 'Config Files'.

Step 4: Look for the 'Level Seed' option. You may enter your seed here.

Step 5: You're all set. Please refer to the note at the top of this page.