I have 93 Nissan Sentra. One of 4 fuel injector is dead. I want to replace the old one. But I do not know how to remove the old one. Do I have to remove the fuel rail to remove the bad fuel injector?

Thank you in advance

You are absolutely correct on that. Any time you remove an injector from a multi-port system the fuel rail needs to come off. Make sure that you disconnect the battery so you don't blow yourself up.