How to edit Junk Email Filter Blocked Domains

How do you edit Junk Email Filter Blocked Domains? I go to the Junk email filter manager, select Block Domain and select Edit. It then opens a window that says Block Domain for the Rule Name: and there is a Filter by "From" contains ( ... and I think all my selected domains to block are there, however, I can't actually change, add or delete the domains shown there. How do I modify the list?