If you have pixels of a mixed gradient along an uneven surface (gradient tool won't be suitable) like say a varying mix of red and black, but you want to change those few pixels to be blue and black instead, is there a way to simply do this?

I asked a friend and he said
>Select:Color Range
>turn the fuzzyness all the way down, and then make sure your sample size is a single pixel
but he's using a different version of photoshop with different terms and I'm too much of an autist to understand exactly what he means.

What do I do exactly? I need the starting part of the instructions explained in a way I can understand. Illustrated would be ideal, please and thanks.