Change a sphere into a cube? (7)
I believe the answer is:
reshape
'into a cube?' is the definition.
I can't judge whether this defines the answer.
'change a sphere' is the wordplay.
'change' is an anagram indicator.
'a'+'sphere'='asphere'
'asphere' with letters rearranged gives 'RESHAPE'.
(Other definitions for reshape that I've seen before include "Give different form to" , "Change the form of" .)