Just to add to this, I had a closer look and the Instagram images are all for the widget in the footer, which while showing the 12 most recent images from Instagram at 50x50, loads them at 640x640 and then resizes them with CSS.
The 12 large images add 874Kb to the page payload, whereas if they were loaded at the size displayed they'd be a total of 20Kb for all 12.
It's as simple as changing the URL for the image, from (for example)
http://scontent.cdninstagram.com/t51...86930432_n.jpg to
http://scontent.cdninstagram.com/t51...86930432_n.jpg
Note the change from s640x640 to s50x50 in the image address.
I don't know where that's set, maybe in an Instagram plugin you have installed, or in the theme widget somewhere, but if that can be changed it's a simple change that would make a big difference.
You should also optimise the images that Google is saying should be done (the ones hosted locally). You can download them already optimised from the pagespeed results page (just let me know if you want me to do it for you, FOC

).