Attempt to improve some wine circle (4)
I believe the answer is:
redo
'attempt to improve' is the definition.
(do again in an attempt to improve)
'some wine circle' is the wordplay.
'some wine' becomes 'red' (red is a type of wine).
'circle' becomes 'O' (O is a circle).
'red'+'o'='REDO'
(Other definitions for redo that I've seen before include "Perform (action) again" , "Have second thoughts" , "Start again" , "further attempt?" , "Make anew" .)