Replacing the SIM card in your iPhone 4S is easy. All you will need is an SIM card eject tool or a small paper clip. Follow this guide to replace or remove your SIM card.
Use a SIM card eject tool or a paperclip to eject the SIM card and its holder.
Remove the SIM Card tray assembly from the iPhone.
Remove the SIM card from its recess in the SIM card tray.