The thumbnail shown in the catalogue is automatically generated.  You can also upload your own thumbnail. The uploaded image will automatically resize and replace the previous one.

• Click on the more… to get into edit mode (see previous paragraph) of the thumbnail you want to replace.
• Proceed with Replace thumbnail.

• Select Use Picture to get the Add file option
• Click Browse and select an image
• Continue with Update

NOTE: You might need to refresh your browser cache before the image is shown.