Real Dictionary

improve
verb: If a skill you have improves or you improve a skill, you get better at it.
verb: If something improves or if you improve it, it gets better.
verb: If you improve after an illness or an injury, your health gets better or you get stronger.
verb: If you improve on a previous achievement of your own or of someone else, you achieve a better standard or result.

improve in American English
to use profitably or to good advantage
intransitive verb: to increase in value, excellence, etc.; become better
transitive verb: to bring into a more desirable or excellent condition

improve in British English
noun
verb: to make or become better in quality; ameliorate