1. download SuperNET lite client http://www.supernet.org/download.php (SuperNET Lite 3.0)
2. use it to send your superBTCD to the ICO site (with the client you can send BTCD to a NXT address or a regular BTCD address)

btw, mgwBTCD is old, nowadays it is called SuperBTCD. If you still have mgwBTCD I think it can be swapped somehow. If you have let me know and I'll find out.

btw2, this is the working technology build on top of Nxt that SuperNET finished. (just a side note )