Incorrect sizing

Hi there

I currently had all my images resized at ‘770 x 600 large’ . Since updating the plugin, all the images are incorrectly resized to a smaller size despite the correct setting.

Do I need to update my wordpress account to version 4.4 or can I revert to the previous version of this plugin?

Thanks!

https://ww.wp.xz.cn/plugins/simple-image-sizes/