Error 504 Gateway Timeout

For the past hour, I have been updating images on my website https://www.whatthebuff.com. I was replacing my 425×375 images with 1000×300 images and I when I attempted to save the last image (I successfully saved 4 posts right before with replacement images w/o an error), I received an “Error 504 Gateway Timeout” message.

I’ve never received this error message before and I’m freaking out trying to figure out how to fix it. I get the same error message when I try to visit my site (www.whatthebuff.com) or the backend (www.whatthebuff/wp-admin), so I can’t even get into the backend to try and see what’s wrong.

I’ve refreshed the page, waited 40 minutes and it’s still not working. My website is down and I need to fix it right away before visitors start noticing (if they haven’t already). I don’t know why it happened, does the image size possibly have anything to do with it? I don’t think it’s my server either because I have another site hosted on it that is working fine.

Someone please help!!