Change, alter (6)
I believe the answer is:
revise
This clue is a double definition.
'change' is the first definition.
(I've seen this in another clue)
'alter' is the second definition.
(I've seen this in another clue)
(Other definitions for revise that I've seen before include "Mug up" , "Go over studies again before exam" , "Study, learn" , "Edit" , "Go back over lesson" .)