Dame Edna, almost wrecked, improved (7)
I believe the answer is:
amended
'improved' is the definition.
('amend' can be a synonym of 'improve')
'dame edna almost wrecked' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'wrecked' indicates anagramming the letters.
'dame'+'edna'='dameedna'
'dameedna' with its last letter taken off is 'dameedn'.
'dameedn' with letters rearranged gives 'AMENDED'.
(Other definitions for amended that I've seen before include "Edited" , "Correct, improve" , "Carried out reforms" , "Put right" , "Revised or altered" .)