There is treatment available - Microdermabrasion, punch grafting, laser resurfacing, etc
Will the scars lighten after long time?
If they are permanent scars, there is no treatment available. If, however, you are referring to the red marks which last a long time after acne pimples go away, then you should ask a dermatologist for treatment to keep you from getting new marks, so you won't have to wait them out. And please don't pick or squeeze them.
Best.
Dr. Rockoff