@jimbrosburrito
If you truly need to swap your SIM card (i.e. presuming it was lost or stolen or has become inoperable) follow @computergeek541 information.
If you are perhaps looking to change your plan from the current one to another, when logged into yourself serve, tap plan and add-ons on the left, then you can change your plan there.
Once you have decided the plan you wish to move to, it is recommended to change on next renewal as opposed to doing an immediate plan change. Doing an immediate plan change will forfeit the items left on your current plan.
