[Theme: Scylla Lite] how to adjust post (image box) size

i have been troubleshooting and researching for hours and i still cant figure out how to change the post image box size. i just want to make it square (being a rectangle, it’s not so image friendly). also the image gets cut off when uploaded.

how would you make the height of the image box taller, so it’s more square?

is it possible you cant modify it?

if you don’t know what i mean, i took a picture: https://oi49.tinypic.com/2yjyqlu.jpg