I have high-resolution pictures but they seem blurred

The app can use the highest-resolution version of your pictures available in your Shopify admin. To take advantage of that, please select the following option in the app preferences page (Zoom preferences):

If after this change you still see the images as blurred, it is possible that they are not stored in Shopify in the highest-resolution version. That can happen if you used an app or tool to upload the pictures or if you tried an app for image optimization. Uploading the images again should fix the issue.