How can one remove old insect bite scars on the legs?

The most common side effect, for those patients affected by bug bites on their legs, is long standing post inflammatory hyperpigmentation.  Another not uncommon reaction is a benign scar formation called a dermatofibroma. Usually patients don't have many dermatofibromas so they probably don't occur after every single bug bite.Neither of these conditions is easy to treat. Some hyperpigmentation cases resolve in a year or two, others need hi dose lightening cream prescribed for them. It is not uncommon that a laser or liquid nitrogen makes it look worse because the center lightens, but the periphery of the dark circle darkens and enlarges. Sometimes prescription creams and cortisone injections can help but there are risks of adverse side effects. Dark spots on legs can be difficult to treat and there is no guarantee that they won't look worse after treatment.

These scars can be improved with a combination of lasers, Aerolase, microneedling/prp, skin lightening, peels, and skin care. Sun protection is essential. I recommend getting a formal evaluation with a scarring expert. Best, Dr. Emer

The good news about scar treatment is that they can always be improved. Pigmented scars can be lightened, red and purple scars can be corrected, depressed scars can be raised, raised scars can be flattened and scar texture can improve. The reality is, it often takes multiple types of treatment to address each aspect of the scar, and even with great improvements, scars will never fully be gone. 
Lasers can help change the pigment, red or purple color and texture of the scar. Fillers and mechanical subcision can be used to raise depressed scars. Various injectable treatments can flatten scars. The right combination of those treatments will depend on your individual needs, goals and anatomy. It takes an expert in scar revision to help choose and present your options, and you need someone who has all of those mentioned treatment modalities available. 
To ensure you are receiving the highest level of care, seek out a modernly trained, new-school dermatologic surgeon, oculoplastic surgeon, facial plastic surgeon or plastic surgeon who is board certified and fellowship trained in one of these "core four" cosmetic specialties. Membership in organizations like the American Academy of Facial Plastic and Reconstructive Surgery help to identify a highly trained surgeon.
Cameron Chesnut
#realself500 Physician

I see these leg scars often and begin treatment with topical Luminase and Exfolase creams, followed by MelaPeel treatments to reduce the pigmentation. The process may take 3 to 6 months.  Our office specializes in scar treatments in Los Angeles. Raffy Karamanoukian MD FACS

The best way to remove old scars depends on what the scar looks like. A red scar can be treated with a pulse dye laser. A brown scar can be treated with a Q-Switched Ruby or Alexandrite laser. A depressed scar can be treated with a variety of injection fillers or fat transfer and/or subcision. And, an elevated scar can be treated with injections of triamcinalone and/or 5% % Flurouracil.

It may be very difficult to fade your dark spots.  Tretinoin cream, glycolic acid and hydroquinone can help with some fading but it does take a long time.  You can try using a waterproof makeup to camouflage the dark spots. 

It is difficult to say specifically without examining you.  If they are red, they  may be amenable to some lasers. If they were open wounds that needed to heal secondarily, they might be amenable to excision.

Dear Ehramonique,
I presume the scars you are refering to are dark marks left behind after an insect bite. This is called post-inflammatory hyperpigmentation and can follow any injury to the skin. I find the best way to lighten this dark color is a combination of a 4% hydroquinone cream used at home and a series of superficial TCA peels done at your dermatologist's office.
Best wishes for your success,
Dr Carr

" I have old scars in my legs caused by insect bites. I'm terribly uncomfortable to go to the beach. "
The appearance of a scar depends on many factors such as mechanism of injury, mode of repair (or not), location on the body, age of the patient, type of skin, ethnicity, did the wound become infected etc.
Unfortunately, scars cannot be removed -- although in many cases they may be made better and less noticeable by scar revision.
Good Luck.