How do change the alternator on a 2000 Mercury Sable?

Unless you're comfortable taking apart a lot of stuff, bring it to the mechanic. If you have the dual overhead engine (which I am assuming), your alternator is located under the engine. Access can be found through the passenger side wheel well. You have to pull out the splash guard and do take out everything in the way. If it's located on top, simply disconnect your battery, take off the belt, disconnect the connectors, pull a few bolts... it's pretty self explanatory.