PrestaShop 1.6.x. How to regenerate thumbnails

Thumbnails regeneration you suppose to do every time you upload images and change image sizes.
  1. Log into your PrestaShop admin panel and go to Preferences -> Images.
  2. Find Regenerate thumbnails button there.
  3. From the drop-down menu select a type of images that should be regenerated – product images, categories images, etc.
  4. Click Regenerate thumbnails button. All the thumbnails will be re-built for you.

Hopefully, this tutorial was helpful for you.