Paint.NET :: Resizing High Quality Pictures?

Im getting married and took some pictures with my fiance so we can create a save the date to send out. Her brother was the photographer who has a very expensive and high quality camera. Took those pictures and opened them in paint.net. these pictures open up to be about 75 by 45. I might be trying to do the impossible but im trying to get it down to be able to fit on a 4x6 picture but everytime and way i try it always seem to pixelate it.