the sticky at the top of the united forum explains how to do it with itasoftware.

United.com is a mess which United has conceded in various meetings. It's being redone, but who knows when the new booking engine will launch.

by the way, if you really want to demonstrate how screwed up it is, try to check the cost of a business class ticket from the first screen, something United should want you to do. I believe you have to go to full fare search, to get a price for a business class fare