The Collaborative International Dictionary of English v.0.48:

Improve \Im*prove"\, v. i.
   1. To grow better; to advance or make progress in what is
      desirable; to make or show improvement; as, to improve in
      health.
      [1913 Webster]

            We take care to improve in our frugality and
            diligence.                            --Atterbury.
      [1913 Webster]

   2. To advance or progress in bad qualities; to grow worse.
      "Domitian improved in cruelty." --Milner.
      [1913 Webster]

   3. To increase; to be enhanced; to rise in value; as, the
      price of cotton improves.
      [1913 Webster]

   To improve on or To improve upon, to make useful
      additions or amendments to, or changes in; to bring nearer
      to perfection; as, to improve on the mode of tillage.
      [1913 Webster]