I am not sure what software you are using, but you are trying to shrink your picture, but keep the same quality right?
IF so, try sizing it by using Bicubic.
That usually helps keep the picture the same, but just smaller. Also, what I do to resize, is I will go down to like, 50%, then resize again, by 50%, etc.
Sometimes, it is just hard to keep the pictures detailed.
Hope this helps!