get up vs change posture

get up and change posture both are verbs.

Word	Noun	Adjective	Verb	Adverb
get up	No	No	Yes	No
change posture	No	No	Yes	No

As verbs, change posture is a hypernym of get up; that is, change posture is a word with a broader meaning than get up:

get up (verb)	change posture (verb)
get up and out of bed	undergo a change in bodily posture
cause to rise
put on special clothes to appear particularly appealing and attractive
develop
study intensively, as before an exam
arrange by systematic planning and united effort
raise from a lower to a higher position
rise to one's feet