thumbnail size

There are two ways to adjust the thumbnail size. The first, and default way, is to change the default thumbnail size in your WordPress media settings. If you don’t want to use that thumbnail size or you’d like the images to be a different size or proportioned different than normal post thumbnails, you can use the option on the Book Reviews options page for Book Cover Size.

Thank you for your reply.
My default thumbnail size is 150×150 and it works in other scenario.
In “Book review plugin” ->option->book cover size I tested the two options:use 16:9 book cover size (133×200) and thumbnail default size but unfortunately the thumbnail size in the widget is always 36×36.
Thank you

Oh, I’m sorry, I didn’t realize you were talking about the widget.

The thumbnail size in the widget cannot be changed. It was developed that way specifically because of the limited space requirements of most sidebars/widgetized areas and images that were any bigger than that caused problems with the text formatting of the listed items.

but I would to enlarge the thumbnail, all the others (eg article’s thumbnail) are 150px. I think that this is a limit for the plugin.
Thank you

It is not possible to change or edit the image size in the widget. You would need to build your own widget with a custom image size.