OK, so I upgraded to 11.0.9 last night and the Server Health Monitor still indicates a problem. Apache memory usage was at 25% last night it's at 43% this morning. So it looks like the nginx component (which I installed through updates & settings as advised) has not solved the problem.
There are some suggestions about editing the config file, I can find it with SSH using putty but it is not clear how to actually edit the file. Any advice?