1999 Ford Taurus My Alternator is shot, I need directions f

The car stopped running one day so we went under the hood and diagnosed the car. The alternator isn't charging completely, there are 11.5 volts going by it and there should be 14. My wife is nagging at me to fix it and I need some instruction of what to do.

What I have done so far
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Charged the battery

I need to know either how to replace the thing or what to do with it.

Thanks in advanced