How to lighten up the dark scars on my skin?

Scar Treatments. Depending on how old they are you may benefit from bleaching creams, steroid injections, silicone gel, lasers or additional surgery. Consult with a physician who specializes in scarring to discuss the best options for you.
Numerous options. First avoid any sun exposure with sun block and minimize inflammation or irritation which can produce post-inflammatory hyper pigmentation. Peels and/or bleaching cream containing hydroquinone, retin-a, and triamcinolone are commonly used. If due to increased vasculature, lasers may be useful as well. Silicone gel sheeting and pressure as well as injected steroids may also be lighten/flatten scars.
Depends on condition. Melasma is a darkening of skin from increased concentration of melanin in the dermis of the skin in that area. It is difficult to treat and camouflage makeup often works best. Freckling or solar lentigos can be bleached with hydroquinone but will return with unprotected sun exposure. See a dermatologist to know if some lasers or medications can help lighten the areas.