An image editor would do. Looking closer, I don't think you can re-antialias them. I'm guessing you (or someone) just did a fill on the original white images to make the blue ones, and the white ones had been anti-aliased, so the edges were "fuzzy". So the fill didn't fill close enough, and left the white fringes. I've taken the liberty of loading them into Gimp and upped the threshold for the flood fill quite a bit so it would match more of the white variants. I've attached the new images here if you'd like to use them. Hope you don't mind.
BTW, I left some white bits on the black images. Not sure if that's what you'd want, but they can be easily filled in to blue if you wish. I thought the knight's eye, for instance, wouldn't make sense to be blue, as it would appear to be a hole in its head!