Change form (6)
I believe the answer is:
mutate
'change form' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for mutate that I've seen before include "Undergo cellular change" , "Me taut? (anag) - change fundamentally" , "Undergo alteration in form" , "Gradually change form" , "Alter genetically" .)