Image sizes NextGEN Basic Slideshow

Hello, I’m trying to do a slideshow for my photography web page,
When I choose the option NextGEN Basic Slideshow and then I go to “Customize the display settings” I can set the Maximum dimension of the image that here is already setted to 600×400 I would like bigger images but when I set the new value for example 1600×1071 and I save everything I go to View the page the slideshow is there and it works but the image is still of the same size. What I have to do ? Thank you very much. Eva.

https://ww.wp.xz.cn/plugins/nextgen-gallery/