How to set image upload size limits

Hi, we've set the WP media sizes to a max (http://prntscr.com/aisy03) however upon uploading images, they are not resized to what we've set: http://prntscr.com/aisxm7
How can we force WP to reduce the image's size minding proportions? we've tried Imsane, but it causes conflicts with our site.
Thanks!