Skin is one of the hardest parts of the body to fix or correct. Sometimes you can go too far and the skin looks fake. Or you leave it alone and you see the aging of the picture, scratches stains or.
When cleaning up skin you do have to be careful not to change the person's looks completly.
Below there is a couple of links to help you.
How to Make a Professional Human Face Retouch in Photoshop
How to Change Skin Tone in Photoshop
If you try either link, I would love to see the original and the edited picture.
Let us know how it worked for you.