WordPress Image Management. No more Thumbnails.

I am running the Sela Theme (1.0.10) as Child Theme. I also use 2 plugins: Jetpack (3.8.0) and Polylang (1.7.12) with 2 languages. That’s it.
I use the standard WordPress Media uploader. I have uploaded only around 30 images on the website, but the image folder already weights 100MB. Each of my originally uploaded images only weights around 500KB. So, I discovered that for each image I upload, WordPress automatically creates 10 thumbnails (4 default, 6 from Sela) which I do not think I ever use. If I do, I do not know how to check this. I know I can stop WordPress from creating standard thumbnails (Media Settings -> Put two zeros) but I do not think this is the right way to go.
So, how can I stop WordPress from creating all these thumbnails? Can Thumbnails be created only if actually used? Can I use Aqua Resizer to do this? If so, how can I stop Sela from creating all this thumbnails for every image? (e.g. I have a Sela_Logo_thumbnail for each image. It just does not make sense.)
Thanks and sorry for the frustrated post.