Ok, lets open the photo you want to change color.
Here is a photo i'll be working with, and what I want to change in here is her blue shirt.
So select the lasso
tool or any other selection tool you feel comfortable with, and make a selection AROUND the object you want to change the color of. It do not need to be a precise selection, just around the edges, like below:
Now create a new adjustment layer, for hue/saturation: go to Layer->New Adjustment Layer->Hue/Saturation. Name it whatever you want then just click OK.
In the Edit option at the top in the Hue/Saturation box, select the "color family" of the color you want to change. (your color may not be listed, but just choose something close). For the above image, the shirt is blue, so I'll select "Blues" under that option.
Then move your cursor onto the object you want to change color, and it'll change into "color picker" icon, just click on the color you want to change to select the color.
Now move your "Hue" slider and the color of your select object will magically change.
Now, if you run into trouble, such as the color OUTSIDE your intended object (but within your selection) changes too, for example: something like this:
Then you just need to move the slider at the bottom of the hue/saturation box until that area turns back into its natural color.
