Improve, augment (7)
I believe the answer is:
enhance
I believe this clue is a double definition.
'improve' is the first definition.
(I know that enhance is a more specific form of improve)
'augment' is the second definition.
(I've seen this before)
(Other definitions for enhance that I've seen before include "Improve the quality of (something)" , "improve things" , "Increase in power" , "Heighten, intensify" , "Boost" .)