I had frequent pimples and acne a couple of the years ago. And now iam having the black traces left behind. What can I do to make them fade or disappear?

Hydroquinone. That's called postinflammatory hyperpigmentation - quite a mouthful, but it simply means a collection of pigment at the site of an old inflammatory process, such as acne. Lightening creams containing hydroquinone are available otc and by prescription, but insurance does not cover them - and never use them at concentrations higher than 4% - higher concentrations sometimes make the darkening worse.
See a dermatologist. A dermatologist may be able to offer some treatments that will help.