I just finished talking with go-today.com, where I booked this trip. The lady I spoke to claimed FRA is one of the "easiest" airports to navigate. At any rate, it will cost more than $1000 to change the flight. So, it will probably be cheaper to pay for one night of hotel in Frankfort than to change the flight. She confirmed to me that UA 927 is a code share with Lufthansa. If we do miss the connecting flight, who should I talk to, Lufthansa or UA?