Hi,
This means that you filled the "images width" and "images height" options of the Hikashop configuration with a small value. Because of that, the original images were resized to that size when you uploaded them.
So you'll have to empty those fields and reupload your images and it should then display with the original resolution on the product page when you click on the image.
Then, you can increase the thumbnails size on the product page/listings with the thumbnails height/width and image on product page height/width options of the Hikashop configuration.