How to delete all the resized images without plugin


Images on my wordpress site are talking 1.4 gb space. I’m sure Used Original images space is not more than 300-400mb. So i want to remove resized images so my site’s backup can be light. i used many image cleaner plugins and only 100mb space reduced. At the end when i checked upload folder in file manager i’m still seeing resized images for every original image. Any new working method ? Thanks