Have you activated the service already and obtained a temporary number? If not, I would suggest going that route first rather than port during activation. Otherwise, if something goes wrong, you get no service in general. Doing the two step process will at least have the service going even if porting fails.
As for porting itself, you do it in the self serve portal. The information required to port is the name on the old account, old account number (no dots, no dashes, no spaces, no special characters, just account number), phone number to be ported. That is about it. The porting itself can take a couple of hours to complete. The best thing to do is continue to keep the SIM from the old provider in the phone. Once you see the old service stop, you know the porting is complete. Here is a thread from the community forum on porting. It is a bit long but has useful information along with user experiences.
http://productioncommunity.publicmobile.ca/t5/Getting-Started/How-do-I-move-my-cell-phone-number-to-...
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