How do I get a new sim card

First make sure you’re phone isn’t ‘sim-locked’, if it is, it won’t work with another carrier.

If it’s not sim-locked, simply contact the carrier of your choice and get the subscription or prepaid service you want, and they will give you a new SIM card. If you do it online or over the phone, they have to know your phone model, so that they can send you the correct sim type (micro etc).