I'd like to change the standard post text size (body text) to a larger size. Sorry for the noob question, but I do find it difficult to do this with most WordPress themes, and hope to save a lot of time by asking a dumb question here.

you can play with the 'font-size' property by adding a css insert at ATO->Add HTML/CSS Inserts->Add CSS Inserts like this

.post-bodycopy {
  font-size: 24px;
{

juggledad - Thanks a bunch - this worked fine. I like a bigger font.