wp-content/uploads folder is using too much space.

In disk space, Web is using 125GB. I think it’s because of the wp-content/upload folder, it is using almost the same amount of space. In wp-content/upload folder I saw every image has 8/9 versions of different sizes (e.g. one image has several sizes like 100*100, 150*150 etc) and I didn’t create those different versions. Now my question is how should I reduce the space used by that folder? Do I have to delete those different versions of images and if so how will I do that cause there are more than 2million images?