Easiest way is to just take a taxi coming out of baggage claim

but is gonna cost you around 100 euros, if not more because of the time.
There is a shuttle that takes you from Malpensa to Stazione Centrale (central train station) for only 5 euros/person... from there, you can take the Metropolitana (subway) to San Siro area... FERMATA LOTTO (Lotto stop) is where you want to go... at least that's the nearest to the Stadium, but check where your hotel is, you maybe closest to the Fair area...