Changed mine twice a few years ago, new alternator failed during warranty
on my Multijet, its not a difficult job, just a complete pain in the backside
, the alternator which is at the top of the engine has to come out the bottom.
The process involves removing the nsf inner wheel arch and engine covers to get to the belts, separating the exhaust as you have to undo the rear lower engine mounting the rock the engine forward to make room to lower the alternator down the back of the engine, it did it all on my back on a driveway, the most difficult bit due to having big hands was disconnecting the electric connections on the rear of the alternator.
If you have the possibility of borrowing a ramp or lift then it should make the job a lot easier.
The first change took me the best part of a day to do, the second was a few hours.
Not sure of the amp rating of the alternator, I got mine through ADP in Gloucester for around a £100 but that was around 2010/11 time.