improve vs alter

improve and alter both are verbs.

Word	Noun	Adjective	Verb	Adverb
improve	No	No	Yes	No
alter	No	No	Yes	No

As verbs, alter is a hypernym of improve; that is, alter is a word with a broader meaning than improve:

Other hypernyms of improve include change, modify.

improve (verb)	alter (verb)
get better	remove the ovaries of
to make better	become different in some particular way, without permanently losing one's or its former characteristics or essence
	cause to change; make different; cause a transformation
	insert words into texts, often falsifying it thereby
	make an alteration to