You should be able to change them online. As you are booked in J fare class for LHR-MUC you are entitled to free seat selection.
Thank you.
There must be something wrong with my booking (through AA), because when I phoned BA, the agent also had trouble making a change. She was able to assign seats, but I still cannot make any changes myself online.
A followup question:
I believe my aircraft will be an A320. Apparently, Row 1 is blocked. When are these seats released for assignment? Any suggestions on getting these seats?