Thanks for reaching out! I understand you are looking to standardize the size of all your images. Are you using one of our free themes by Shopify found here, or a third-party theme? If you are using a third-party theme, they may have different image upload requirements and ratios, and it would be best to check with the theme developers directly. If you are using a Shopify theme, you can upload images of up to 4472 x 4472 pixels with a file size of up to 20 MB. With any Shopify themes, we typically recommend using 2048 x 2048 pixels for square product photos. These sizes allow for high-resolution images for a professional look with great zoom capabilities. That being said, for zoom functionality to work, your images have to be more than 800 x 800 pixels. You can read more about adding product media here, and more on how to use our image editor here.
If after you reference these guides, you are still having issues, feel free to share your store URL here and we would be happy to take a closer look.