Change models? Not very often (6)
I believe the answer is:
seldom
'not very often' is the definition.
(I've seen this before)
'change models?' is the wordplay.
'change' is an anagram indicator.
'models' is an anagram of 'SELDOM'.
(Other definitions for seldom that I've seen before include "Alluvium" , "Only occasionally" , "Once in a blue moon" , "on rare occasions" , "Not very often, rarely" .)