Have a word with Ilexa or Gendan, they might be able to accept that one in as a trade-in, I did that years ago with VAG-COM, sorry if one of the above links implies that .
Bottom line could be, make contact with your original supplier as it is them that should be best placed to help you upgrade.
Edit:- Revo's posting did direct you to Ross Tech "trade in conditions etc" - try what I've suggested with your original VCDS reseller - same situation will apply there.