You can TRY bringing them up in "My Itineraries" on United.com; there should be a link on each leg of the trip for "Fare rules." These aren't the full rules, of course ... and even more "of course," United.com very frequently chokes and refuses to display them.

Another way to see them is to do a dummy booking of the same trip on Expedia and choose the "Fare rules & restrictions" link to display them. Make sure the fare booking code is the same as the one your ticket is booked as; for some trips, this may mean playing with the dates on your dummy booking to get the fare to show up (like if your original fare was a 14-day advance purchase one and you are trying to see if 7 days out, or if it has time or day restrictions, etc.)

Or you can go to Travelocity and see a list of all fare codes for that city pair and then view the rules.