Mine went far from home so I had to have it done by a mechanic.
When I did the timing belt I made up a tool to release the acessory belt tension (working from above).
I used a 15mm flex head ratcheting ring spanner cut off one end and extended with a steel tube.
Overall 500mm long. The locking pin is 3mm diameter.
Alan Howatt's video shows the alternator removal:
https://www.youtube.com/watch?v=QDBXyCAAURc
I plan to do the other car myself soon. Mine don't have the fuel filter in the way, it's at the rear.
I started dismantling the old alternator and the slip rings/brushes are seriously gone, hard to believe it kept going so long.