Newbie question: How to insert/remove a SIM?

Hey: A very basic newbie question. I have a Verizon iPhone 5S, how do I remove the Verizon SIM and insert an AT&T Various SIM? What is a Various SIM? And does the Various SIM needs to be cut to a smaller size SIM? Or will the AT&T Various SIM is already small enough? I know once I receive the SIM from AT&T. First, I need the SIM number that starts with "89", and than second go to att.com/activations

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