PrestaShop 1.6.x. How to change predefined images dimensions

1. In your PrestaShop admin panel go to Preferences -> Images section:
2. You can see images for different sections and their dimensions.
3. Click on the image name. Change Width and Height. Save the changes. Do the same actions for other images: 
4. In Preferences -> Images go to Regenerate thumbnails section and click Regenerate thumbnails button to regenerate images: 
5. Refresh the page to see the changes. You may have to clear browser cache and cookies.

Hopefully, this tutorial was helpful for you.