First off, to reduce scarring, never squeeze zits. If a pimple does leave a red or brownish mark it should eventually go away on its own. Be patient -- it could take a year or more.
If your acne is under control but past pimples have left scars, there are things your dermatologist can do to help get rid of them.
The best treatment will depend on the type of scar and how bad it is. But these treatments aren't usually recommended for teens. Your dermatologist can give you more information.