Any way I can upgrade with miles to Biz class?
If you log in to your reservation on United.com it will probably show an offer such as 50,000 miles and $600 or some other figure (NOT a good deal!), on FlyerTalk certain users are reporting offers at the time of online check-in of under $1000 for MXP flights, perhaps less at the checkin machine...
All these fares are low fare classes (non pun intended)
and can not be upgrade via United GPUs or SWUs (the usual upgrade instruments)...
so again if you want to upgrade, look at your reservation on United.com to see if there are any offers or hope for luck on day of travel...