1990 Lexus LS 400 replace alternator

I had a few warning lights come on in my Engine and and I check all my fluid levels and they were fine/ I drove home which was only few miles and my car died right before I made it home. Then it was like the battery wasn't holding a charge. I took it to schucks and they said the battery was fine but alternator needed replace. I got one at wreaking yard in great condition but need to know how to replace it. My friend does work on cars but I thougt a step by step guide would be helpful! :)