Earphones shut off speakers but do not convey sound.

Earphones work in other devices but not in the macbook, and it is difficult to extract. We are afraid to plug it in again because we think the receptacle is bent or defective and the sound may stop working on the speakers as well if we stick in another plug. I think it needs a new socket but do not know how to replace it. Is it a user fixable operation? Must the computer be opened? And if so, how? I have worked on other computers, but not this type. If I knew how to get inside, I could probably fix it if it's just the jack that's defective. Thanks.