Skeetendo

I'm currently working on a private project, and was planning on adding in some Generation 5 devamp sprites into Pokemon Gold. My problem is that the sprites are too big. I need them to be brought down to size, but resizing them adds in too many colors. I've searched for a guide on resizing sprites without changing them, but to no avail. Does anyone know of a process for correctly resizing sprites? Thank you in advance.