Thank you for your kind replies. These are very useful. I will try and talk to the Lufthansa agents in SFO and see if they can help me.

These were not cheap tickets and the direct SFO->FRA were even more expensive. After I bought them the direct one became even cheaper but they wouldnt let me change (oh well). I figured that usually transfers take about 30 mins so it should be easy. On doing some research it seems it may take about an hour which seems tight.