How to change colors like this? I know it’s probably a stupid question, but i can’t find anything, so i’ll just ask here.
what do you mean, you want to know how to change the colours in that pic?
Use an adjustment layer with mask. Hand paint the areas where you want the effect into the mask.
Your best bet to do this is manual painting. You can try the Select menu -> color range to select certain areas with similar characteristics but there is no telling what you’ll get. Like kesonmis said, adjustment layer and mask it. One of my techniques was to make a new layer set to colour blending mode and to paint on that. Like I said though, comes back to manual work.
Alternatively, try duotone or split-toning. That might make things easier.
Although written for Photoplus, the process is the same for photoshop…
http://www.joblense.com/visuals/photoplus-graphics-tutorial-replacing-colour/