Changing the fluid is simple, repairing the diff isn't quite so simple. What are you trying to accomplish? Your post isn't very clear; you ask how to change the fluid, but then go on to say that there are metal shavings and the shop needs to repair it. What exactly is the problem?
This thread may provide some insight as far as changing the fluid goes. Do a search and you will find tons of info already posted. Also, get a service manual or go to the local public library and copy the pertinent pages out of their service manual or print the info off alldata dependng on what they have.