Size of product Images you can change via Appearance > Customize > WooCommerce > Product Images http://prntscr.com/onfqga (disable crop option for the product grid to show images with proportions you uploaded). After these changes, you need to Regenerate Thumbnails to apply them. Use Regenerate thumbnails plugin to do this – https://wordpress.org/plugins/regenerate-thumbnails/
To change product widget image size go to Settings > Media > Thumbnails Size.
More information about product image settings you can find in WooCommerce Documentation – https://docs.woocommerce.com/document/fixing-blurry-product-images/
