It's a big job.
approx 50% of the forum will tell you that you don't have to drop the subframe. In my experience, don't listen to them, you just make the job 10 times harder for very little time saving.
The dual wisbone suspension setup of the 147 makes it very hard to pop the driveshafts out of the box. I prefer to remove the suspenstion and hub carriers completely but this is also very time consuming.
Remove the inlet manifold for easy access to the starter motor. Remove the subframe to give you room to get the gearbox out. Take your time and while you are at it, inspect and replace where necessary the antiroll bar bushes, droplinks and front wishbones. Always do the clutch including release bearing while you are in there.
Budget a long weekend to do it and if you don't have a good quality hex (6 sided) socket set and long breaker bar then don't even attempt it. You will need some odd sizes like 24mm and 18mm as well.
Alfa GT 3.2 V6 - Daily Driver.
Alfa 145 QV ph1 in green (Death by rust project) For Sale.
Alfa GTV TS ph2 in blue