What flight and date is this?
It looks like you have had a change of aircraft type to a
"77L". There's no first class on these 777 variants so there's no risk of you being booted out of your seat if it stays a 77L.
OTOH there could always be another aircraft change nearer to departure, as BA are short of long haul aircraft at the moment. So on balance I would stay where I am if I was happy with it.