featured images same size

Hi,
I’m having issues with the featured images sizes as you can see…
I wanted to change size of them and I used Simple Images Size plugin, I probably touched something wrong as now they are ALL different..

I’m using Savona Edge. I know probably I need to ask to the Theme forum but nobody replies there.

Unfortunately Savona Edge has got a lot of images sizes:
-Thumbnail size
-Medium size
-Large size
-medium_large size
-savona-slider-full-thumbnail size
-savona-full-thumbnail size
-savona-grid-thumbnail size
-savona-single-navigation size

Which one should I use???

Also, in almost each one is asked if I want to crop it and there is a tick box saying ‘showing in post insertion?’
For me is too much confusing, particularly after I’ve been spending days changing sizes and obtaining either nothing or a mess-up of all the file sizes..

If someone could help me I would be very grateful.
Thank you

The page I need help with: [log in to see the link]