To make something better; to enhance its quality, condition, or performance. She took a course to improve her language skills.
To increase the value, attractiveness, or usefulness of something, especially by making additions or adjustments. The company plans to improve its product line to attract more customers.
To become better; to advance toward a more desirable state. His health improved after the surgery.
To achieve a better result than something previous; to surpass — usually used with "on" or "upon". She improved on her previous time by nearly a minute.