Why would we have instructions on doing that? I thought people just died. (and their allocations kept climbing and climbing until they own the whole server...)
Just kidding. Theoretically you should be able to use the "DNS" link on manage domains to point to the nameservers of your new host. (Basically use the directions that we use to point GoDaddy domains to DH servers, but backwards.)
Hope this is decent advice, if not, my name is rlparker.