I'm looking to travel to London in the Fall, meeting my wife after a work event. What I want to do is book a ticket that is upgradeable to Business and use miles for the upgrade. I've looked on the UA website and see you can select "upgradeable fare" types.

Here are my questions:

1. Once I buy the upgradeable ticket, is it automatically upgraded using the appropriate mileage needed? Or do I have to wait a certain amount of time for it to clear?

2. What are the chances of me getting the upgrade? I'd hate to pay the higher fare only to be told that upgrades aren't available on that flight.

3. Is it possible to have them just upgrade 1 portion of the trip? Since I"d be meeting my wife in London, she would look unkindly to me being in Business on the way back while she's stuck in the back.

Thanks in advance for any answers.

Bob