speed up vs modify

speed up and modify both are verbs.

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

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

Other hypernyms of speed up include alter, change.

speed up (verb)	modify (verb)
move faster	make less severe or harsh or extreme
cause to move faster	add a modifier to a constituent
	cause to change; make different; cause a transformation