Improve half of them to finish with (5)
I believe the answer is:
emend
'improve' is the definition.
(I know that emend is a type of improve)
'half of them to finish with' is the wordplay.
'half of' means to take half the letters.
'to' is a charade indicator (letters next to each other).
'finish with' becomes 'end' (synonyms. I am not sure about the 'with' bit.).
'them' with half the letters taken is 'em'.
'em'+'end'='EMEND'
Can you help me to learn more?
(Other definitions for emend that I've seen before include "Improve by altering" , "Make correction in written material" , "do editorial work" , "Improve (texts)" , "make an improvement" .)