Increase image resolution without increasing dimensions

Site URL: https://gregorylassale.com/

I'm not very happy with how pixelated the icons look on this page:

https://gregorylassale.com/english#services

I do have higher resolution PNGs of those images, as well as SVG files. Unfortunately, the latter format isn't supported and posting high resolution PNGs makes the icons larger, which I don't want. I actually want to make them smaller, but more important increase their higher resolution.

Resizing the images with blocks is clunky and it's almost impossible to get the dimensions I want. The icons end up being too big or too small. When I reduce resize the files in Preview on macOS, the icons end up pixelated.

Could someone let me know how to resize the image files without losing resolution, or a way to resize the images directly inside Squarepsace while retaining granular control over their dimensions, or alternatively whether there is a way to use the SVG versions instead?

Much appreacted. 

I figured out how to display SVG files with code blocks.

Thx