Heighten (7)
I believe the answer is:
enhance
'heighten' is the definition.
(I know that enhance is a more specific form of heighten)
This is all the clue.
(Other definitions for enhance that I've seen before include "Increase attractiveness of, improve" , "Improve quality (of item)" , "Improve the value of (something)" , "Make better or more attractive" , "produce better image" .)