Improve morning and finish (5)
I believe the answer is:
amend
'improve' is the definition.
('amend' can be a synonym of 'improve')
'morning and finish' is the wordplay.
'morning' becomes 'am'.
'and' means one lot of letters go next to another.
'finish' becomes 'end' ('end' can be a synonym of 'finish').
'am'+'end'='AMEND'
(Other definitions for amend that I've seen before include "Put right" , "Change, alter" , "Alter in detail" , "Rectify" , "Make small changes to" .)