Alter some Images and replace current thumbnail images on wordpress website

I need a large quantity of product images altered so that they are all the same square thumbnail size, in jpg. There are 3028 images in total which need this treatment, and preferably they would also be uploaded to our website to replace the current images as part of this job. The website uses wordpress with woo commerce installed for managing this large range of musical instrument products. The website is [login to view URL] Currently you can see an example of our image problems at [login to view URL] - they are all different sizes and many are very pixellated. When you select a product from this page, the next image is also a problem - see [login to view URL] as an example. However, the single product image close-up (third click) seems to be ok in all instances. All our images need to be re-sized so that they are square with a white background. They need to show the entire image within that square, not cut off the way they currently are. I currently have the woo commerce/wordpress image settings as follows, all with hard crop selected: Catalog images 212 x 212 Single product image 500 x 500 Product thumbnails 90 x 90 I don't really know what these settings should be or what would be the best size for the thumbnails, so I need assistance to get this right so that the images and site look more professional. Although I have tried adjusting the settings in wordpress and woo commerce according to the woo commerce instructions, as well as regenerating thumbnails, it doesn't seem to make any difference to those problem images.