The most common and most likely answer to this crossword clue is the 11 letter word REDECORATED
I've seen this crossword clue in The Daily Telegraph
R
E
D
E
C
O
R
A
T
E
D
Buddy explains!

The straight part
We know that "smartened up again" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case smartened up again = redecorated.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
REDECORATED verb- To change the appearance of a place by altering the decor.
- To refurbish.