replace all straight quotes with curly quotes

I'm frequently given large blocks of text where all the quotes are straight. What is the easiest way to change all open and closing quotes to curly?

Currently I use find and replace - the closing quote is easy since it's usually after either an , or . but the opening quotes are more difficult to find and replace, though many can be found and replaced by simply looking for a quote with a space before.

Is there an easier way to "curly" them all in one go, or a macro to do it?