Troubleshooting Pinterest Button

I installed a social plugin called Social Sharing Toolkit.

In terms of the Pinterest button, whenever it is clicked it pins the featured image from the post – however, it pins the thumbnail version of the featured image, not the large-size image on the page.

Can anyone suggest how I can fix this so it doesn’t pin the thumbnail but the full size image?

The way my site is setup, I need to set a featured image for each post for the home page excerpts.

Thanks!