Sparkle Themes

Hi there,

Thanks for using our theme, we really appreciate your business

You can see below step to change the category image size.

go to WordPress Dashboard >> WooCommerce >> settings >> Product above tab >> and see below different sub tab again click on display tab below you have options to change category and product image size. when you can change size then agin upload image or use this plugins https://wordpress.org/plugins/regenerate-thumbnails/ and again re-generate you upload image.

also see below screenshot.