This tutorial will give you a good introduction to the color replacement tool. It's always best to start out with a simpler image as far as clear distinct color 'separation' to make the selection easier that you would like to change color on.

Go ahead and first drag the background layer to the new layer icon so you can change pixels on a copied layer.

Now go to Image: Adjustments: Replace Color.

This will bring up the Replace Color dialog box. Go ahead and drag the cursor outside of the dialog box to get your eyedropper tool. Now click on a a color that you would like to change.

When you click, the color will be shown in the Color: box (where you can also change it manually but that's kind of silly here).

Now go ahead and adjust the 'Fuzziness' value. Just think of this as a way to get a sharper or fuzzier 'selection' based on brightness. You could see it as a realtime preview of tolerance settings in a way. You are selecting a color and the lower the fuzziness, the sharper your selections (white) and deselections (black) will be. If you bring fuzziness way down to zero everything will be more deselected (black for no replacement) and far to the right it will be more selected based off of your initial clickpoint and it's color/brightness value.

Creating a higher fuzziness make the selection more apt to choosing different pixel colors in the range, basically creating a really large tolerance setting that starts to become really ineffective for most images. What you want to do is raise the fuzziness and then bring it down so just the area you selected in the 'Selection' Preview is as white as possible.

White means it is selected in the preview box and black is what's deselected. What shows as white is the area that you have selected to replace the color on.

Go ahead and keep clicking on different parts of the image and you'll notice that the selection preview keeps changing. This is because you are choosing different shades of a color. It will show the same pixel selection across the entire image. Each time you click on the normal eyedropper you will restart another selection.

On the bottom of the dialog box you can get a realtime preview of your replace color itself, whereas the top you can keep working on the color 'range' selection. Go ahead and click on the color box down there and choose a different color (or drag the hue slider). With 'Preview' on you can immediately see the results of your color range selection in progress. You can then continue making adjustments (after you press OK here).

The higher the fuzziness = more of the image selected (the lighter areas first because we started with a lighter color). You will see the replace color start to bleed through on areas such as the lighter part of his shirt.

 

This is why you want to get a nice contrast between white and black with white being your chosen color range selection so you can distinguish and isolate it from the rest of the image and the other color ranges remained untouched with the replacement (the darker they are).

Now try choosing add to eyedropper selection (the middle eyedropper). This will allow you to keep clicking on different areas that you would like to 'add' to your selection to replace color with. You can use it to click on slightly darker shades and it will update in realtime in the preview window.

You can also try Subtract from color range eyedropper to deselect certain color ranges (which will show the realtime preview in the selection window).  Just be careful when doing this; ultimately get the area you want to change color so it's selected very well.  Don't be afraid to use the add to or subtract from eyedroppers; just click where you want to add or subtract a color to the final color range selection to be replaced.  It won't show all of the different color stops you are choosing, just the preview as it updates.