let up vs modify

let up and modify both are verbs.

Word	Noun	Adjective	Verb	Adverb
let up	No	No	Yes	No
modify	No	No	Yes	No

As verbs, modify is a hypernym of let up; that is, modify is a word with a broader meaning than let up:

Other hypernyms of let up include alter, change.

let up (verb)	modify (verb)
become less in amount or intensity	make less severe or harsh or extreme
reduce pressure or intensity	add a modifier to a constituent
	cause to change; make different; cause a transformation