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
We take care to improve in our frugality and
2. To advance or progress in bad qualities; to grow worse.
"Domitian improved in cruelty." --Milner.
3. To increase; to be enhanced; to rise in value; as, the
price of cotton improves.
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.