Delete unused thumbnails and retina images

Hello,

I have a blog/site that is 10 years old and photo-heavy (more than 8,000 I believe). I also use a theme that creates lots of thumbnails. However, not all thumbnails are used to all pictures, far from it (most only need one or two thumbnails). Also, for a while, I had the "retina friendly" option of my theme checked.

I recently realized that I was running out of space on my server, and it was because of the sheer number of images generated for each picture uploaded, there are 14 thumbnails times two (so 28) because it also generated their retina counterparts, for each one of them.

I've been trying to find a way to clean that up a little bit, but all the plugins that I find looking on Google don't seem to do the trick (they see that all the thumbnails are registered so they leave them alone).

Is there a way to delete all images that are not actually used on the site (all the registered thumbnails that have been generated when the images were uploaded but that have never been used)? The only plugin I found that seemed to do it hasn't been updated in four years (and it's only partially automated), so I'm not too confident using it.

I'd also like to delete all the retina images (all ending with @2x.jpg). That only would save a lot of space on my server, even if I can't manage to delete the unused thumbnails.

Could anyone help?

Thanks in advance.

Disclaimer: my technical skills are basic. I can use Wordpress's backend fine, but I can't code much and while I understand database, I'm not sure how to handle them)