Improve hospital in Cornish town with no parking zone (7)
I believe the answer is:
enhance
'improve' is the definition.
(enhancing is a kind of improving)
I can't explain the rest of the clue.
(Other definitions for enhance that I've seen before include "Increase in power" , "Improve quality (of item)" , "Boost" , "lift" , "Improve, make more attractive" .)