Robin, when you see that, you should go to the Edit post Gear icon...then you should be able to click or hover on the huge photo and see a choice for "Edit"- and if you click edit you can then change the size either by changing the pixel dimension number, or as Dusty said by dragging one diagonal corner 'handle' in or out diagonally. The handle looks like a tiny square.
P.S. - sorry I did not see this thread earlier!
Those irritated by grain of sand best avoid beach.
-Strumelia proverb c.1990
updated by @strumelia: 01/29/16 01:45:48PM