Theme calling for Full Size images

Hi,

Is there a way to make this theme call for an image’s ‘large’ or ‘medium’ counterpart? In my old theme, the images automatically called to a smaller dimension version of itself, and therefore the loading time on the page was a lot faster.

My old theme still exists through wordpress.com (not wordpress.org) and it calls to the same image in almost the same way, but with ?w=550&h=413 on the end of the url

New theme: Request URL:https://wherefoodis.files.wordpress.com/2015/03/p3034792.jpg

Old theme: Request URL:https://wherefoodis.files.wordpress.com/2015/03/p3034792.jpg?w=550&h=413

I know I should have uploaded my original images in a smaller dimension, but I have 3 years worth of photos like this, and I can’t possibly change all posts manually. Is there a fix for this?

Thank you 🙂