Where the feck do people get their ideas?
Frank Ford's site is very good. His advice is mostly excellent.
That said, if you are even a tiny bit uncertain then don't touch the truss rod. Just take it into the shop and let a pro do it.
On my £100 Chinese acoustic I tweak the rod with confidence as and when I need to (which is actually hardly ever). On a Martin I would be very careful and a little nervous.
Take it to a decent guitar tech. The adjustment, if it is just the rod, will be quick and cheap - and if done by a pro it will also be safe.