If it due to a tan this will eventually wear off. If tyou are a dark-skinned individual then it is difficult to treat the whole body and reduce pigmentation.
There are skin lightening agents available which can be used on areas of hyperpigmentation, but these will be only on some parts due to some predisposing factors.
They are Hydroquinone 2-4%, Creams containing Azelaic acid or Kojic acid and also Vit A based ointment called Tretinoin. Any of these, single or combined can be used on areas of hyperpigmentation, but they mah have side effects of redness, burning, itching etc.
Please do consult with a doctor if you should experience any of these.