Easiest way to remove acne scars and marks from your photo is to use the spot healing brush in Photoshop. To use this tool, all you have to do is select the spot healing brush and make it a little bigger than the mark/scar you want to remove and just click on it. After that, you will immediately see a difference. That's really all there is to it.
Some more points about the Spot Healing brush
1. It works better when you just click on a spot as compared to clicking and dragging,
2. The Spot Healing Brush takes the information from the area surrounding the area covered in the circle,
3. If you don't like the result, you can click again and every time, it will create a different result,
4. But if you undo and click on the same spot, most likely, it will generate the same result it did earlier,
5. Keep adjusting the size of the brush according to the size of the mark you are trying to remove.
For a simple tutorial you can watch the following video
