IMPORTANT : Before start of this tutorial you should install some of the Adobe Photoshop versions by buying it in online store. All informations you can find on Adobe official website : http://www.photoshop.com
Step 1 : Select image which you wont to fix, made right mouse click and when menu appear select Open With > Adobe Photoshop CS3 (or other higher version). You can also always open your picture directly from Photoshop with click on File and then Open... menu.
Step 2 : If your picture is open and appear on the screen now is time to chose tool which will help you to remove all scars and acnes. From the menu on the left side of screen (maybe your tools menu will be on some other place) select with a left mouse click "Spot Healing Brush Tool". On the top you should have Brush menu and it is up to you to set the right Brush diameter (as larger scars/acne are as larger diameter will be used).
Step 3 : Now when "Spot Healing Brush Tool" is selected and diameter is set you should try to clean skin using the left mouse click part by part. Made a left click on every scar/acne at the image which you wont to remove (sometime will be necessary to click more times in the way of getting cleaner color). At the end you can simply save your image on File and then Save... from the menu.