Power off the iPhone
Locate the SIM tray on the side of the iPhone
Insert a SIM eject tool or a straightened paperclip into the small hole next to the tray
Press gently until the tray pops out
Pull the SIM tray out completely
Remove the SIM card from the tray
Reinsert the empty tray or a new SIM card tray back into the iPhone
Power the iPhone back on