You just need to change the image size to a suitable size at Customize > WooCommerce > Product Images
change the ‘Thumbnail Width’ to an appropriate size, so for example if you have 3 products per row then the thumbnail width would need to be larger than if you are displaying 6 products per row.
But, if a suitable width would be 400px for example, and your original images are only 350px width then they will of course appear low quality because they are being resized upwards.
Also, if you have a mixture of images that are tall and narrow and others that are more square, then you can try the 1:1 ‘Thumbnail cropping’ which will crop images into a square shape.