PrestaShop 1.7. How to edit predefined image dimensions

1. In your PrestaShop admin panel go to Design -> Image Settings section: 
2. You will see the list of predefined image dimensions. You can enable the image size for the specific type of content directly in the image sizes list:
3. Click on the image size which should be regenerated for editing. You can set your own width and height parameters. Save the changes:
4. Once all the desired image dimensions are changed, click the Regenerate thumbnails button at the bottom of the page:
5. Refresh your website to see the changes. It is possible, you’ll need to clear the PrestaShop cache and browser cache.

Add a new image size and define the type of content

1. 1. Go to Design -> Image Settings section. Click the Add new image type button:
   2. You can set the following options:
      • Name for the image type – the title of the new image type;
      • Width – maximum image width in pixels;
      • Height – maximum image height in pixels;
      • Products – the type will be used for Product images;
      • Categories – the type will be used for Category images;
      • Brands – the type will be used for Brand images;
      • Suppliers – the type will be used for Supplier images;
      • Stores – the type will be used for Store images.

1. Save the changes and refresh your website.

Hopefully, this tutorial was helpful for you.