George, this was not an upgrade in my case but a change in flights to an earlier flight.

I was waitlisted to move to an earlier flight. It ended up clearing on the itinerary and had a message in red to call reservations to CONFIRM the change.

Finally got around to checking the itineary, called United and said "sorry, you did not call in time so we put you back on your original flight." But the agent saw I was a 1K and managed to move me, reminding it "It might be good if you have flight changes or upgrades to check, like, Daily."

A Flyertalk friend of mine said the same thing after I shared this story.

It might be tough to check on line daily but maybe it's worth the call or the extra two minutes, daily, on ual.com.