I just did mine and there was an idler pulley accessible from underneath the car that had to be loosened. I also understand that some years need to have the crank pulley taken apart and adjust the belt tension with shims.
the belt is easy.
when youre done, DO NOT take your AC to be serviced by anyone but a Alfa mechanic who worked at the dealership. the Alfa AC unit only needs some freeze12, some Esther100 (oil) and a few schrader-valves to work again. no reciever/dryer, no new compressor.
mine sat unused for 5 years with no belt, and is cold as can be now. costed me 80$